A015845 Numbers k such that phi(k) | sigma(k + 7).

1, 2, 3, 4, 5, 6, 7, 8, 12, 16, 20, 22, 24, 26, 27, 28, 31, 35, 39, 40, 50, 58, 63, 70, 88, 95, 108, 112, 116, 120, 135, 152, 163, 183, 224, 228, 241, 273, 315, 323, 364, 369, 455, 476, 520, 524, 616, 620, 632, 703, 782, 855, 903, 945, 950, 1008, 1124, 1188

Offset: 1

Author

Robert G. Wilson v

Keywords

• nonn

Links

• Ivan Neretin, Table of n, a(n) for n = 1..1000

Programs

Mathematica

Select[Range[3000], Divisible[DivisorSigma[1, 7 + #], EulerPhi[#]] &]  (* David Nacin, Mar 03 2012 *)

PARI

is(n)=!(sigma(n+7)%eulerphi(n)) \\ Charles R Greathouse IV, Sep 25 2012

Extensions

a(1) = 1 inserted by Ivan Neretin, Feb 05 2017