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
Offset: 1
Keywords
Examples
6 is included because phi(6) = 2 divides phi(7) = 6.
Links
- Amiram Eldar, Table of n, a(n) for n = 1..6255 (terms below 10^10)
Programs
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Mathematica
Select[Range[4000], Divisible[EulerPhi[# + 1], EulerPhi[#]] &] (* Amiram Eldar, Jul 13 2019 *)
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PARI
lista(nn) = for (n=1, nn, if (eulerphi(n+1) % eulerphi(n) == 0, print1(n, ", "))); \\ Michel Marcus, Sep 14 2015
Extensions
Offset set to 1 by Michel Marcus, Sep 14 2015
Comments