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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). 1
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified July 25 03:53 EDT 2021. Contains 346283 sequences. (Running on oeis4.)