BBC Russian

A057919

Numbers k such that phi(k) divides phi(k+1), where phi(k) is the Euler totient function A000010.

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: A136291 A128393 A368988 * 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