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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
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
Sequence in context: A136291 A128393 A368988 * A102250 A084788 A002809
KEYWORD
nonn
AUTHOR
Leroy Quet, Nov 11 2000
EXTENSIONS
Offset set to 1 by Michel Marcus, Sep 14 2015
STATUS
approved