login
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.
1
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
MATHEMATICA
Select[Range[500], ! Divisible[EulerPhi[#*(# + 1)*(# + 2)/6], EulerPhi[#*(# + 1)/2]] &] (* Amiram Eldar, Jul 17 2022 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Benoit Cloitre, Jan 28 2002
STATUS
approved