A067544 Numbers k such that phi(k*(k+1)*(k+2)/6)/phi(k*(k+1)/2) is not an integer where phi(k) = A000010(k) is the Euler totient function.

8, 9, 18, 27, 44, 45, 53, 62, 80, 81, 90, 98, 99, 108, 116, 126, 134, 135, 143, 162, 171, 189, 198, 224, 225, 233, 234, 251, 260, 261, 270, 279, 287, 288, 296, 315, 332, 350, 351, 387, 413, 422, 423, 441, 449, 450, 458, 459, 468, 476, 477, 503, 504, 512, 522

Offset

1,1

Comments

Often a(k) == 0 (mod 3) and if a(k+1) - a(k) = 1 then a(k+1) == 0 (mod 3).

Links

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

Mathematica

Select[Range[500], ! Divisible[EulerPhi[#*(# + 1)*(# + 2)/6], EulerPhi[#*(# + 1)/2]] &] (* Amiram Eldar, Jul 17 2022 *)

Crossrefs

Cf. A000010, A000217, A000292, A086700.

Sequence in context: A159836 A230542 A069809 * A022313 A120311 A061414

Adjacent sequences: A067541 A067542 A067543 * A067545 A067546 A067547

Keyword

nonn

Author

Benoit Cloitre, Jan 28 2002

Status

approved