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 A057919 Numbers k such that phi(k) divides phi(k+1), where phi(k) is the Euler totient function A000010. 2
 1, 2, 3, 4, 6, 12, 15, 16, 18, 36, 72, 90, 96, 104, 108, 154, 162, 164, 192, 194, 255, 256, 286, 364, 432, 486, 495, 576, 584, 702, 768, 792, 804, 924, 975, 1066, 1152, 1260, 1296, 1458, 2146, 2204, 2592, 2625, 2834, 2916, 3255, 3382, 3456, 3705, 3888 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS The intersection of this sequence and A057920 is A001274. - Michel Marcus, Sep 14 2015 LINKS Amiram Eldar, Table of n, a(n) for n = 1..6255 (terms below 10^10) EXAMPLE 6 is included because phi(6) = 2 divides phi(7) = 6. MATHEMATICA Select[Range[4000], Divisible[EulerPhi[# + 1], EulerPhi[#]] &] (* Amiram Eldar, Jul 13 2019 *) PROG (PARI) lista(nn) = for (n=1, nn, if (eulerphi(n+1) % eulerphi(n) == 0, print1(n, ", "))); \\ Michel Marcus, Sep 14 2015 CROSSREFS Cf. A001274, A057920. Sequence in context: A034293 A136291 A128393 * A102250 A084788 A002809 Adjacent sequences:  A057916 A057917 A057918 * A057920 A057921 A057922 KEYWORD nonn AUTHOR Leroy Quet, Nov 11 2000 EXTENSIONS Offset set to 1 by Michel Marcus, Sep 14 2015 STATUS approved

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Last modified November 27 07:28 EST 2021. Contains 349365 sequences. (Running on oeis4.)