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

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Last modified June 7 22:39 EDT 2023. Contains 363157 sequences. (Running on oeis4.)