A241207 - OEIS

A241207

Consider a number of k digits n = d_(k)*10^(k-1) + d_(k-1)*10^(k-2) + … + d_(2)*10 + d_(1). Sequence lists the numbers n such that sigma(n)-n = Sum_{i=1..k-1}{sigma(Sum_{j=1..i}{d_(j)*10^(j-1)})} - Sum_{i=1..k-1}{sigma(Sum_{j=1..i}{d_(k-j+1)*10^(i-j)})} (see example below)

23, 47, 142, 161, 433, 1435, 1900, 6679, 48917, 197943, 257941, 3916321, 48635983, 1142976889, 1811878288

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OFFSET

1,1

COMMENTS

a(16) > 10^10. - Giovanni Resta, May 23 2016

LINKS

Table of n, a(n) for n=1..15.

EXAMPLE

If n = 48917, starting from the least significant digit, let us cut the number into the set 7, 17, 917, 8917. We have:

sigma(7) = 8;

sigma(17) = 18;

sigma(917) = 1056;

sigma(8917) = 9196.

Then, starting from the most significant digit, let us cut the number into the set 4, 48, 489, 4891. We have:

sigma(4) = 7;

sigma(48) = 124;

sigma(489) = 656;

sigma(4891) = 5032.

Finally,

8 + 18 + 1056 + 9196 - (7 + 124 + 656 + 5032) = 4459 = sigma(48917) - 48917.

MAPLE

with(numtheory); P:=proc(q) local a, b, k, n;

for n from 2 to q do a:=0; k:=1; while trunc(n/10^k)>0 do

a:=a+phi(trunc(n/10^k)); k:=k+1; od; b:=0; k:=1;

while (n mod 10^k)<n do b:=b+phi(n mod 10^k); k:=k+1; od;

if phi(n)=b-a then print(n); fi; od; end: P(10^9);

CROSSREFS

Cf. A000203, A240894-A240903.

Sequence in context: A042048 A347008 A239563 * A042050 A139857 A139900

Adjacent sequences: A241204 A241205 A241206 * A241208 A241209 A241210

KEYWORD

nonn,base,more

AUTHOR

Paolo P. Lava, Apr 17 2014

EXTENSIONS

a(1)-a(2) corrected and a(12)-a(15) added by Giovanni Resta, May 23 2016

STATUS

approved