A067536 - OEIS

A067536

Numbers k such that phi(k*(k+1)*(k+2)/3)/phi(k) is not an integer where phi(k) is the Euler totient function A000010(k).

9, 45, 81, 99, 135, 225, 234, 261, 288, 351, 423, 450, 459, 477, 504, 567, 585, 639, 666, 819, 837, 855, 900, 927, 954, 981, 1017, 1134, 1179, 1242, 1305, 1359, 1431, 1449, 1485, 1521, 1593, 1638, 1710, 1773, 1908, 1953, 1971, 2025, 2061, 2097, 2151

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OFFSET

1,1

COMMENTS

For every n, a(n)==0 (mod 3).

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

MATHEMATICA

Select[Range[2000], ! Divisible[EulerPhi[#*(# + 1)*(# + 2)/3], EulerPhi[#]] &] (* Amiram Eldar, Mar 01 2020 *)

PROG

(PARI) is(n)=eulerphi(n*(n+1)*(n+2)/3)%eulerphi(n) \\ Charles R Greathouse IV, Mar 05 2013

CROSSREFS

Cf. A000010, A007290.

Sequence in context: A044492 A207359 A243090 * A139609 A321779 A068314

Adjacent sequences: A067533 A067534 A067535 * A067537 A067538 A067539

KEYWORD

nonn

AUTHOR

Benoit Cloitre, Jan 28 2002

STATUS

approved