Displaying 1-10 of 77 results found.
Number of partitions of n into an odd number of parts.
+10
206
0, 1, 1, 2, 2, 4, 5, 8, 10, 16, 20, 29, 37, 52, 66, 90, 113, 151, 190, 248, 310, 400, 497, 632, 782, 985, 1212, 1512, 1851, 2291, 2793, 3431, 4163, 5084, 6142, 7456, 8972, 10836, 12989, 15613, 18646, 22316, 26561, 31659, 37556, 44601, 52743, 62416, 73593, 86809, 102064, 120025, 140736
COMMENTS
Number of partitions of n in which greatest part is odd.
Number of partitions of n+1 into an even number of parts, the least being 1. Example: a(5)=4 because we have [5,1], [3,1,1,1], [2,1,1] and [1,1,1,1,1,1].
Also number of partitions of n+1 such that the largest part is even and occurs only once. Example: a(5)=4 because we have [6], [4,2], [4,1,1] and [2,1,1,1,1]. - Emeric Deutsch, Apr 05 2006 Also the number of partitions of n such that the number of odd parts and the number of even parts have opposite parities. Example: a(8)=10 is a count of these partitions: 8, 611, 521, 431, 422, 41111, 332, 32111, 22211, 2111111. - Clark Kimberling, Feb 01 2014, corrected Jan 06 2021 In Chaves 2011 see page 38 equation (3.20). - Michael Somos, Dec 28 2014 Suppose that c(0) = 1, that c(1), c(2), ... are indeterminates, that d(0) = 1, and that d(n) = -c(n) - c(n-1)*d(1) - ... - c(0)*d(n-1). When d(n) is expanded as a polynomial in c(1), c(2),..,c(n), the terms are of the form H*c(i_1)*c(i_2)*...*c(i_k). Let P(n) = [c(i_1), c(i_2), ..., c(i_k)], a partition of n. Then H is negative if P has an odd number of parts, and H is positive if P has an even number of parts. That is, d(n) has A027193(n) negative coefficients, A027187(n) positive coefficients, and A000041 terms. The maximal coefficient in d(n), in absolute value, is A102462(n). - Clark Kimberling, Dec 15 2016
REFERENCES
N. J. Fine, Basic Hypergeometric Series and Applications, Amer. Math. Soc., 1988; p. 39, Example 7.
FORMULA
G.f.: Sum(k>=1, x^(2*k-1)/Product(j=1..2*k-1, 1-x^j ) ). - Emeric Deutsch, Apr 05 2006 G.f.: - Sum(k>=1, (-x)^(k^2)) / Product(k>=1, 1-x^k ). - Joerg Arndt, Feb 02 2014 G.f.: Sum(k>=1, x^(k*(2*k-1)) / Product(j=1..2*k, 1-x^j)). - Michael Somos, Dec 28 2014
EXAMPLE
G.f. = x + x^2 + 2*x^3 + 2*x^4 + 4*x^5 + 5*x^6 + 8*x^7 + 10*x^8 + 16*x^9 + 20*x^10 + ...
The a(1) = 1 through a(8) = 10 partitions into an odd number of parts are the following. The Heinz numbers of these partitions are given by A026424. (1) (2) (3) (4) (5) (6) (7) (8)
(111) (211) (221) (222) (322) (332)
(311) (321) (331) (422)
(11111) (411) (421) (431)
(21111) (511) (521)
(22111) (611)
(31111) (22211)
(1111111) (32111)
(41111)
(2111111)
The a(1) = 1 through a(8) = 10 partitions whose greatest part is odd are the following. The Heinz numbers of these partitions are given by A244991. (1) (11) (3) (31) (5) (33) (7) (53)
(111) (1111) (32) (51) (52) (71)
(311) (321) (322) (332)
(11111) (3111) (331) (521)
(111111) (511) (3221)
(3211) (3311)
(31111) (5111)
(1111111) (32111)
(311111)
(11111111)
(End)
MAPLE
g:=sum(x^(2*k)/product(1-x^j, j=1..2*k-1), k=1..40): gser:=series(g, x=0, 50): seq(coeff(gser, x, n), n=1..45); # Emeric Deutsch, Apr 05 2006
MATHEMATICA
nn=40; CoefficientList[Series[ Sum[x^(2j+1)Product[1/(1- x^i), {i, 1, 2j+1}], {j, 0, nn}], {x, 0, nn}], x] (* Geoffrey Critzer, Dec 01 2012 *) a[ n_] := If[ n < 0, 0, Length@Select[ IntegerPartitions[ n], OddQ[ Length@#] &]]; (* Michael Somos, Dec 28 2014 *) a[ n_] := If[ n < 1, 0, Length@Select[ IntegerPartitions[ n], OddQ[ First@#] &]]; (* Michael Somos, Dec 28 2014 *) a[ n_] := If[ n < 0, 0, Length@Select[ IntegerPartitions[ n + 1], #[[-1]] == 1 && EvenQ[ Length@#] &]]; (* Michael Somos, Dec 28 2014 *) a[ n_] := If[ n < 1, 0, Length@Select[ IntegerPartitions[ n + 1], EvenQ[ First@#] && (Length[#] < 2 || #[[1]] != #[[2]]) &]]; (* Michael Somos, Dec 28 2014 *)
PROG
(PARI) {a(n) = if( n<1, 0, polcoeff( sum( k=1, n, if( k%2, x^k / prod( j=1, k, 1 - x^j, 1 + x * O(x^(n-k)) ))), n))}; /* Michael Somos, Jul 24 2012 */ (PARI) q='q+O('q^66); concat([0], Vec( (1/eta(q)-eta(q)/eta(q^2))/2 ) ) \\ Joerg Arndt, Mar 23 2014
CROSSREFS
The even-length version is A027187. The case of odd maximum as well as length is A340385. Other cases of odd length:
- A024429 counts set partitions of odd length. - A067659 counts strict partitions of odd length. - A089677 counts ordered set partitions of odd length. - A166444 counts compositions of odd length. - A174726 counts ordered factorizations of odd length. - A332304 counts strict compositions of odd length. - A339890 counts factorizations of odd length. A026804 counts partitions whose least part is odd.
A072233 counts partitions by sum and length.
A101707 counts partitions of odd positive rank.
Number of partitions of n into distinct parts such that number of parts is odd.
+10
85
0, 1, 1, 1, 1, 1, 2, 2, 3, 4, 5, 6, 8, 9, 11, 14, 16, 19, 23, 27, 32, 38, 44, 52, 61, 71, 82, 96, 111, 128, 148, 170, 195, 224, 256, 293, 334, 380, 432, 491, 557, 630, 713, 805, 908, 1024, 1152, 1295, 1455, 1632, 1829, 2048, 2291, 2560, 2859, 3189, 3554, 3958, 4404
COMMENTS
Ramanujan theta functions: phi(q) := Sum_{k=-oo..oo} q^(k^2) ( A000122), chi(q) := Prod_{k>=0} (1+q^(2k+1)) ( A000700).
FORMULA
Expansion of (1-phi(-q))/(2*chi(-q)) in powers of q where phi(),chi() are Ramanujan theta functions. - Michael Somos, Feb 14 2006 G.f.: sum(n>=1, q^(2*n^2-n) / prod(k=1..2*n-1, 1-q^k ) ). [ Joerg Arndt, Apr 01 2014]
EXAMPLE
The a(5) = 1 through a(15) = 14 partitions (A-F = 10..15):
5 6 7 8 9 A B C D E F
321 421 431 432 532 542 543 643 653 654
521 531 541 632 642 652 743 753
621 631 641 651 742 752 762
721 731 732 751 761 843
821 741 832 842 852
831 841 851 861
921 931 932 942
A21 941 951
A31 A32
B21 A41
B31
C21
54321
(End)
MAPLE
b:= proc(n, i, t) option remember; `if`(n>i*(i+1)/2, 0,
`if`(n=0, t, add(b(n-i*j, i-1, abs(t-j)), j=0..min(n/i, 1))))
end:
a:= n-> b(n$2, 0):
MATHEMATICA
b[n_, i_, t_] := b[n, i, t] = If[n > i*(i + 1)/2, 0, If[n == 0, t, Sum[b[n - i*j, i - 1, Abs[t - j]], {j, 0, Min[n/i, 1]}]]]; a[n_] := b[n, n, 0]; Table[a[n], {n, 0, 80}] (* Jean-François Alcover, Jan 16 2015, after Alois P. Heinz *) CoefficientList[Normal[Series[(QPochhammer[-x, x]-QPochhammer[x])/2, {x, 0, 100}]], x] (* Andrey Zabolotskiy, Apr 12 2017 *) Table[Length[Select[IntegerPartitions[n], UnsameQ@@#&&OddQ[Length[#]]&]], {n, 0, 30}] (* Gus Wiseman, Jan 09 2021 *)
PROG
(PARI) {a(n)=local(A); if(n<0, 0, A=x*O(x^n); polcoeff( (eta(x^2+A)/eta(x+A) - eta(x+A))/2, n))} /* Michael Somos, Feb 14 2006 */ (PARI) N=66; q='q+O('q^N); S=1+2*sqrtint(N);
gf=sum(n=1, S, (n%2!=0) * q^(n*(n+1)/2) / prod(k=1, n, 1-q^k ) );
(PARI) N=66; q='q+O('q^N); S=1+sqrtint(N);
gf=sum(n=1, S, q^(2*n^2-n) / prod(k=1, 2*n-1, 1-q^k ) );
CROSSREFS
Numbers with these strict partitions as binary indices are A000069. The Heinz numbers of these partitions are A030059. Other cases of odd length:
- A024429 counts set partitions of odd length. - A089677 counts ordered set partitions of odd length. - A174726 counts ordered factorizations of odd length. - A339890 counts factorizations of odd length. A008289 counts strict partitions by sum and length.
A026804 counts partitions whose least part is odd, with strict case A026832.
Number of even-length factorizations of n into factors > 1.
+10
77
1, 0, 0, 1, 0, 1, 0, 1, 1, 1, 0, 2, 0, 1, 1, 3, 0, 2, 0, 2, 1, 1, 0, 4, 1, 1, 1, 2, 0, 3, 0, 3, 1, 1, 1, 5, 0, 1, 1, 4, 0, 3, 0, 2, 2, 1, 0, 6, 1, 2, 1, 2, 0, 4, 1, 4, 1, 1, 0, 6, 0, 1, 2, 6, 1, 3, 0, 2, 1, 3, 0, 8, 0, 1, 2, 2, 1, 3, 0, 6, 3, 1, 0, 6, 1, 1, 1, 4, 0, 6, 1, 2, 1, 1, 1, 10, 0, 2, 2, 5, 0, 3, 0, 4, 3
EXAMPLE
The a(n) factorizations for n = 12, 16, 24, 36, 48, 72, 96, 120:
2*6 2*8 3*8 4*9 6*8 8*9 2*48 2*60
3*4 4*4 4*6 6*6 2*24 2*36 3*32 3*40
2*2*2*2 2*12 2*18 3*16 3*24 4*24 4*30
2*2*2*3 3*12 4*12 4*18 6*16 5*24
2*2*3*3 2*2*2*6 6*12 8*12 6*20
2*2*3*4 2*2*2*9 2*2*3*8 8*15
2*2*3*6 2*2*4*6 10*12
2*3*3*4 2*3*4*4 2*2*5*6
2*2*2*12 2*3*4*5
2*2*2*2*2*3 2*2*2*15
2*2*3*10
MAPLE
g:= proc(n, k, t) option remember; `if`(n>k, 0, t)+
`if`(isprime(n), 0, add(`if`(d>k, 0, g(n/d, d, 1-t)),
d=numtheory[divisors](n) minus {1, n}))
end:
a:= n-> `if`(n=1, 1, g(n$2, 0)):
MATHEMATICA
facs[n_]:=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[facs[n/d], Min@@#>=d&]], {d, Rest[Divisors[n]]}]];
Table[Length[Select[facs[n], EvenQ@Length[#]&]], {n, 100}]
PROG
(PARI) A339846(n, m=n, e=1) = if(1==n, e, sumdiv(n, d, if((d>1)&&(d<=m), A339846(n/d, d, 1-e)))); \\ Antti Karttunen, Oct 22 2023
CROSSREFS
The case of set partitions (or n squarefree) is A024430. The case of partitions (or prime powers) is A027187. The odd-length factorizations are counted by A339890. A316439 counts factorizations by product and length.
A340102 counts odd-length factorizations into odd factors.
Numbers whose sum of divisors is even.
+10
58
3, 5, 6, 7, 10, 11, 12, 13, 14, 15, 17, 19, 20, 21, 22, 23, 24, 26, 27, 28, 29, 30, 31, 33, 34, 35, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 65, 66, 67, 68, 69, 70, 71, 73, 74, 75, 76, 77, 78, 79, 80, 82
COMMENTS
The even terms of this sequence are the even terms appearing in A178910. [Edited by M. F. Hasler, Oct 02 2014] Numbers k such that the number of odd divisors of k ( A001227) is even. - Omar E. Pol, Apr 04 2016 Numbers k such that the sum of odd divisors of k ( A000593) is even. - Omar E. Pol, Jul 05 2016 Numbers with a squarefree part greater than 2. - Peter Munn, Apr 26 2020 Equivalently, numbers whose odd part is nonsquare. Compare with the numbers whose square part is even (i.e., nonodd): these are the positive multiples of 4, A008586\{0}, and A225546 provides a self-inverse bijection between the two sets. - Peter Munn, Jul 19 2020 Also numbers whose reversed prime indices have alternating product > 1, where we define the alternating product of a sequence (y_1,...,y_k) to be Product_i y_i^((-1)^(i-1)). Also Heinz numbers of the partitions counted by A347448. - Gus Wiseman, Oct 29 2021 Numbers whose number of middle divisors is not odd (cf. A067742). - Omar E. Pol, Aug 02 2022
MATHEMATICA
Select[Range[82], EvenQ[DivisorSigma[1, #]]&] (* Jayanta Basu, Jun 05 2013 *)
PROG
(Python)
from math import isqrt
def f(x): return n-1+isqrt(x)+isqrt(x>>1)
kmin, kmax = 1, 2
while f(kmax) >= kmax:
kmax <<= 1
while True:
kmid = kmax+kmin>>1
if f(kmid) < kmid:
kmax = kmid
else:
kmin = kmid
if kmax-kmin <= 1:
break
CROSSREFS
Cf. A030059, A335433, A335448, A339890, A344607, A347438, A347443, A347445, A347446, A347452, A347453, A347465.
Number of balanced factorizations of n.
+10
42
1, 1, 1, 0, 1, 0, 1, 1, 0, 0, 1, 2, 1, 0, 0, 1, 1, 2, 1, 2, 0, 0, 1, 1, 0, 0, 1, 2, 1, 3, 1, 1, 0, 0, 0, 2, 1, 0, 0, 1, 1, 3, 1, 2, 2, 0, 1, 2, 0, 2, 0, 2, 1, 1, 0, 1, 0, 0, 1, 2, 1, 0, 2, 1, 0, 3, 1, 2, 0, 3, 1, 3, 1, 0, 2, 2, 0, 3, 1, 2, 1, 0, 1, 2, 0, 0, 0, 1, 1, 2, 0, 2, 0, 0, 0, 3, 1, 2, 2, 2, 1, 3, 1, 1, 3, 0, 1, 3, 1, 3, 0, 2, 1, 3, 0, 2, 2, 0, 0, 4
COMMENTS
A factorization into factors > 1 is balanced if it is empty or its length is equal to its maximum Omega ( A001222).
EXAMPLE
The balanced factorizations for n = 120, 144, 192, 288, 432, 768:
3*5*8 2*8*9 3*8*8 4*8*9 6*8*9 8*8*12
2*2*30 3*6*8 4*6*8 6*6*8 2*8*27 2*2*8*24
2*3*20 2*4*18 2*8*12 2*8*18 3*8*18 2*3*8*16
2*5*12 2*6*12 4*4*12 3*8*12 4*4*27 2*4*4*24
3*4*12 2*2*2*24 4*4*18 4*6*18 2*4*6*16
2*2*3*16 4*6*12 4*9*12 3*4*4*16
2*12*12 6*6*12 2*2*12*16
2*2*2*36 2*12*18 2*2*2*2*48
2*2*3*24 3*12*12 2*2*2*3*32
2*3*3*16 2*2*2*54
2*2*3*36
2*3*3*24
3*3*3*16
MATHEMATICA
facs[n_]:=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[facs[n/d], Min@@#>=d&]], {d, Rest[Divisors[n]]}]];
Table[Length[Select[facs[n], #=={}||Length[#]==Max[PrimeOmega/@#]&]], {n, 100}]
PROG
(PARI) A340653(n, m=n, mbo=0, e=0) = if(1==n, mbo==e, sumdiv(n, d, if((d>1)&&(d<=m), A340653(n/d, d, max(mbo, bigomega(d)), 1+e)))); \\ Antti Karttunen, Oct 22 2023
CROSSREFS
Positions of nonzero terms are A100959. The co-balanced version is A340596. Taking maximum factor instead of maximum Omega gives A340599. The cross-balanced version is A340654. The twice-balanced version is A340655. A045778 counts strict factorizations.
A316439 counts factorizations by product and length.
A320655 counts factorizations into semiprimes.
Other balance-related sequences:
- A010054 counts balanced strict partitions. - A047993 counts balanced partitions. - A098124 counts balanced compositions. - A106529 lists Heinz numbers of balanced partitions. - A340597 have an alt-balanced factorization. - A340598 counts balanced set partitions. - A340600 counts unlabeled balanced multiset partitions. - A340656 have no twice-balanced factorizations. - A340657 have a twice-balanced factorization.
Number of factorizations of n with integer alternating product.
+10
39
1, 1, 1, 2, 1, 1, 1, 2, 2, 1, 1, 2, 1, 1, 1, 4, 1, 2, 1, 2, 1, 1, 1, 2, 2, 1, 2, 2, 1, 1, 1, 4, 1, 1, 1, 6, 1, 1, 1, 2, 1, 1, 1, 2, 2, 1, 1, 5, 2, 2, 1, 2, 1, 3, 1, 2, 1, 1, 1, 2, 1, 1, 2, 8, 1, 1, 1, 2, 1, 1, 1, 6, 1, 1, 2, 2, 1, 1, 1, 5, 4, 1, 1, 2, 1, 1, 1, 2, 1, 3, 1, 2, 1, 1, 1, 6, 1, 2, 2, 6, 1, 1, 1, 2, 1, 1, 1, 7
COMMENTS
A factorization of n is a weakly increasing sequence of positive integers > 1 with product n.
We define the alternating product of a sequence (y_1,...,y_k) to be Product_i y_i^((-1)^(i-1)).
EXAMPLE
The factorizations for n = 4, 16, 36, 48, 54, 64, 108:
(4) (16) (36) (48) (54) (64) (108)
(2*2) (4*4) (6*6) (2*4*6) (2*3*9) (8*8) (2*6*9)
(2*2*4) (2*2*9) (3*4*4) (3*3*6) (2*4*8) (3*6*6)
(2*2*2*2) (2*3*6) (2*2*12) (4*4*4) (2*2*27)
(3*3*4) (2*2*2*2*3) (2*2*16) (2*3*18)
(2*2*3*3) (2*2*4*4) (3*3*12)
(2*2*2*2*4) (2*2*3*3*3)
(2*2*2*2*2*2)
MATHEMATICA
facs[n_]:=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[facs[n/d], Min@@#>=d&]], {d, Rest[Divisors[n]]}]];
altprod[q_]:=Product[q[[i]]^(-1)^(i-1), {i, Length[q]}];
Table[Length[Select[facs[n], IntegerQ@*altprod]], {n, 100}]
PROG
(PARI) A347437(n, m=n, ap=1, e=0) = if(1==n, if(e%2, 1==denominator(ap), 1==numerator(ap)), sumdiv(n, d, if((d>1)&&(d<=m), A347437(n/d, d, ap * d^((-1)^e), 1-e)))); \\ Antti Karttunen, Oct 22 2023
CROSSREFS
Allowing any alternating product <= 1 gives A339846. Allowing any alternating product > 1 gives A339890. The restriction to powers of 2 is A344607. The even-length case is A347438, also the case of alternating product 1. Allowing any alternating product < 1 gives A347440. Allowing any alternating product >= 1 gives A347456. A046099 counts factorizations with no alternating permutations.
A071321 gives the alternating sum of prime factors of n (reverse: A071322).
A273013 counts ordered factorizations of n^2 with alternating product 1.
A347460 counts possible alternating products of factorizations.
Cf. A025047, A038548, A062312, A088218, A119620, A316523, A330972, A332269, A347445, A347447, A347451, A347454.
Number of unordered factorizations of n with alternating product 1.
+10
37
1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0
COMMENTS
Also the number of unordered factorizations of n with alternating sum 0.
Also the number of unordered factorizations of n with all even multiplicities.
This is the even-length case of A347437, the odd-length case being A347441. An unordered factorization of n is a weakly increasing sequence of positive integers > 1 with product n.
We define the alternating product of a sequence (y_1,...,y_k) to be Product_i y_i^((-1)^(i-1)).
EXAMPLE
The a(n) factorizations for n = 16, 64, 144, 256, 576:
4*4 8*8 12*12 16*16 24*24
2*2*2*2 2*2*4*4 2*2*6*6 2*2*8*8 3*3*8*8
2*2*2*2*2*2 3*3*4*4 4*4*4*4 4*4*6*6
2*2*2*2*3*3 2*2*2*2*4*4 2*2*12*12
2*2*2*2*2*2*2*2 2*2*2*2*6*6
2*2*3*3*4*4
2*2*2*2*2*2*3*3
MATHEMATICA
facs[n_]:=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[facs[n/d], Min@@#>=d&]], {d, Rest[Divisors[n]]}]];
altprod[q_]:=Product[q[[i]]^(-1)^(i-1), {i, Length[q]}];
Table[Length[Select[facs[n], altprod[#]==1&]], {n, 100}]
PROG
(PARI) A347438(n, m=n, k=0, t=1) = if(1==n, (1==t), my(s=0); fordiv(n, d, if((d>1)&&(d<=m), s += A347438(n/d, d, 1-k, t*(d^((-1)^k))))); (s)); \\ Antti Karttunen, Oct 30 2021
CROSSREFS
Positions of nonzero terms are A000290. The restriction to powers of 2 is A035363. Positions of non-1's are A213367 \ {1}. Sorted first positions are 1, 2, and all terms of A330972 squared. Allowing any alternating product <= 1 gives A339846. Allowing any alternating product > 1 gives A339890. Allowing any integer alternating product gives A347437. Allowing any integer reciprocal alternating product gives A347439. Allowing any alternating product < 1 gives A347440. Allowing any alternating product >= 1 gives A347456. A046099 counts factorizations with no alternating permutations.
A071321 gives the alternating sum of prime factors (reverse: A071322).
A316524 gives the alternating sum of prime indices (reverse: A344616).
A344606 counts alternating permutations of prime factors.
A347441 counts odd-length factorizations with integer alternating product.
A347460 counts possible alternating products of factorizations.
Cf. A000041, A005117, A025047, A038548, A062312, A088218, A316523, A332269, A344607, A347442, A347446, A347463.
Number of co-balanced factorizations of n.
+10
30
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 2, 1, 1, 1, 3, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 4, 1, 1, 1, 3, 1, 1, 1, 2, 2, 1, 1, 4, 1, 2, 1, 2, 1, 3, 1, 3, 1, 1, 1, 4, 1, 1, 2, 1, 1, 1, 1, 2, 1, 1, 1, 5, 1, 1, 2, 2, 1, 1, 1, 4, 1, 1, 1, 4, 1, 1, 1, 3, 1, 4, 1, 2, 1, 1, 1, 5, 1, 2, 2, 4, 1, 1, 1, 3, 1, 1, 1, 5, 1, 1, 1, 4, 1, 1, 1, 2, 2, 1, 1, 8
COMMENTS
We define a factorization of n into factors > 1 to be co-balanced if it has exactly A001221(n) factors.
EXAMPLE
The a(n) co-balanced factorizations for n = 12, 24, 36, 72, 120, 144, 180:
2*6 3*8 4*9 8*9 3*5*8 2*72 4*5*9
3*4 4*6 6*6 2*36 4*5*6 3*48 5*6*6
2*12 2*18 3*24 2*2*30 4*36 2*2*45
3*12 4*18 2*3*20 6*24 2*3*30
6*12 2*4*15 8*18 2*5*18
2*5*12 9*16 2*6*15
2*6*10 12*12 2*9*10
3*4*10 3*3*20
3*4*15
3*5*12
3*6*10
MATHEMATICA
facs[n_]:=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[facs[n/d], Min@@#>=d&]], {d, Rest[Divisors[n]]}]];
Table[Length[Select[facs[n], Length[#]==PrimeNu[n]&]], {n, 100}]
PROG
(PARI) A340596(n, m=n, om=omega(n)) = if(1==n, (0==om), sumdiv(n, d, if((d>1)&&(d<=m), A340596(n/d, d, om-1)))); \\ Antti Karttunen, Jun 10 2024
CROSSREFS
Positions of terms > 1 are A126706. The version for unlabeled multiset partitions is A319616. The alt-balanced version is A340599. The cross-balanced version is A340654. The twice-balanced version is A340655. A045778 counts strict factorizations.
A316439 counts factorizations by product and length.
Other balance-related sequences:
- A010054 counts balanced strict partitions. - A047993 counts balanced partitions. - A098124 counts balanced compositions. - A106529 lists Heinz numbers of balanced partitions. - A340597 lists numbers with an alt-balanced factorization. - A340598 counts balanced set partitions. - A340600 counts unlabeled balanced multiset partitions. Cf. A003963, A006141, A050320, A112798, A117409, A324518, A339846, A339890, A340607, A340656, A340657.
Heinz numbers of integer partitions of odd positive rank.
+10
29
3, 7, 10, 13, 15, 19, 22, 25, 28, 29, 33, 34, 37, 42, 43, 46, 51, 52, 53, 55, 61, 62, 63, 69, 70, 71, 76, 77, 78, 79, 82, 85, 88, 89, 93, 94, 98, 101, 105, 107, 113, 114, 115, 116, 117, 118, 119, 121, 123, 130, 131, 132, 134, 136, 139, 141, 146, 147, 148, 151
COMMENTS
The Dyson rank of a nonempty partition is its maximum part minus its number of parts. The rank of an empty partition is 0.
The Heinz number of a partition (y_1,...,y_k) is prime(y_1)*...*prime(y_k). This gives a bijective correspondence between positive integers and integer partitions.
EXAMPLE
The sequence of partitions with their Heinz numbers begins:
3: (2) 46: (9,1) 82: (13,1)
7: (4) 51: (7,2) 85: (7,3)
10: (3,1) 52: (6,1,1) 88: (5,1,1,1)
13: (6) 53: (16) 89: (24)
15: (3,2) 55: (5,3) 93: (11,2)
19: (8) 61: (18) 94: (15,1)
22: (5,1) 62: (11,1) 98: (4,4,1)
25: (3,3) 63: (4,2,2) 101: (26)
28: (4,1,1) 69: (9,2) 105: (4,3,2)
29: (10) 70: (4,3,1) 107: (28)
33: (5,2) 71: (20) 113: (30)
34: (7,1) 76: (8,1,1) 114: (8,2,1)
37: (12) 77: (5,4) 115: (9,3)
42: (4,2,1) 78: (6,2,1) 116: (10,1,1)
43: (14) 79: (22) 117: (6,2,2)
MATHEMATICA
rk[n_]:=PrimePi[FactorInteger[n][[-1, 1]]]-PrimeOmega[n];
Select[Range[100], OddQ[rk[#]]&&rk[#]>0&]
CROSSREFS
Note: Heinz numbers are given in parentheses below.
These partitions are counted by A101707. A001222 gives number of prime indices.
- Rank -
A257541 gives the rank of the partition with Heinz number n.
A340653 counts balanced factorizations.
- Odd -
A339890 counts factorizations of odd length.
A340101 counts factorizations into odd factors.
A340102 counts odd-length factorizations into odd factors.
Cf. A001221, A006141, A056239, A112798, A168659, A200750, A316413, A325134, A340601, A340602, A340608, A340609, A340610.
Number of factorizations of n with integer reciprocal alternating product.
+10
29
1, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 3, 0, 1, 0, 1, 0, 0, 0, 1, 1, 0, 1, 1, 0, 0, 0, 3, 0, 0, 0, 4, 0, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 3, 1, 1, 0, 1, 0, 1, 0, 1, 0, 0, 0, 1, 0, 0, 1, 6, 0, 0, 0, 1, 0, 0, 0, 5, 0, 0, 1, 1, 0, 0, 0, 3, 3, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 1, 0, 0, 0, 3, 0, 1, 1, 4, 0, 0, 0, 1, 0, 0, 0, 5
COMMENTS
All of these factorizations have an even number of factors, so their reverse-alternating product is also an integer.
A factorization of n is a weakly increasing sequence of positive integers > 1 with product n.
We define the reciprocal alternating product of a sequence (y_1,...,y_k) to be Product_i y_i^((-1)^i).
The value of a(n) does not depend solely on the prime signature of n. See the example comparing a(144) and a(400). - Antti Karttunen, Jul 28 2024
EXAMPLE
The a(n) factorizations for
n = 16, 36, 64, 72, 128, 144:
a(n) = 3, 4, 6, 5, 7, 11
--------------------------------------------------------------------------------
2*8 6*6 8*8 2*36 2*64 2*72
4*4 2*18 2*32 3*24 4*32 3*48
2*2*2*2 3*12 4*16 6*12 8*16 4*36
2*2*3*3 2*2*2*8 2*2*3*6 2*2*4*8 6*24
2*2*4*4 2*3*3*4 2*4*4*4 12*12
2*2*2*2*2*2 2*2*2*16 2*2*6*6
2*2*2*2*2*4 2*3*3*8
3*3*4*4
2*2*2*18
2*2*3*12
2*2*2*2*3*3
For n=400, there are 12 such factorizations:
2*200
4*100
5*80
10*40
20*20
2*2*2*50
2*2*5*20
2*2*10*10
2*4*5*10
2*5*5*8
4*4*5*5
2*2*2*2*5*5.
Note that 400 = 2^4 * 5^2 has the same prime signature as 144 = 2^4 * 3^2. 400 = 2*4*5*10 is the factorization for which there is no analogous factorization of 144, as 2*3*4*6 doesn't satisfy the condition of having an integer reciprocal alternating product.
(End)
MATHEMATICA
facs[n_]:=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[facs[n/d], Min@@#>=d&]], {d, Rest[Divisors[n]]}]];
recaltprod[q_]:=Product[q[[i]]^(-1)^i, {i, Length[q]}];
Table[Length[Select[facs[n], IntegerQ[recaltprod[#]]&]], {n, 100}]
PROG
(PARI) A347439(n, m=n, ap=1, e=0) = if(1==n, !(e%2) && 1==denominator(ap), sumdiv(n, d, if(d>1 && d<=m, A347439(n/d, d, ap * d^((-1)^e), 1-e)))); \\ Antti Karttunen, Jul 28 2024 (PARI) A347439(n, m=0, ap=1, e=1) = if(1==n, 1==denominator(ap), sumdiv(n, d, if(d>1 && d>=m, A347439(n/d, d, ap * d^((-1)^e), 1-e)))); \\ Antti Karttunen, Jul 28 2024
CROSSREFS
Positions of 0's are A005117 \ {1}. Positions of non-0's are 1 and A013929. Positions of 1's are 1 and A082293. Allowing any alternating product <= 1 gives A339846. Allowing any alternating product > 1 gives A339890. The non-reciprocal version is A347437. Allowing any alternating product < 1 gives A347440. The non-reciprocal reverse version is A347442. Allowing any alternating product >= 1 gives A347456. The restriction to perfect squares is A347459, non-reciprocal A347458. A038548 counts possible reverse-alternating products of factorizations.
A046099 counts factorizations with no alternating permutations.
A071321 gives the alternating sum of prime factors (reverse: A071322).
A316524 gives the alternating sum of prime indices (reverse: A344616).
A273013 counts ordered factorizations of n^2 with alternating product 1.
A347441 counts odd-length factorizations with integer alternating product.
A347460 counts possible alternating products of factorizations.
Cf. A236913, A316523, A330972, A332269, A344606, A344607, A347445, A347446, A347454, A347457, A347463.
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