A015837 Numbers k such that phi(k) | sigma(k + 2).

1, 2, 3, 4, 5, 9, 10, 12, 13, 18, 21, 22, 25, 28, 36, 38, 40, 42, 45, 52, 55, 58, 60, 90, 93, 108, 112, 117, 130, 152, 153, 156, 175, 180, 182, 187, 208, 222, 226, 228, 246, 258, 264, 280, 306, 310, 313, 380, 396, 468, 490, 504, 532, 592, 609, 628, 700, 715

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, 2 + #], EulerPhi[#]] &] (* David Nacin, Mar 03 2012 *)

PARI

isok(n) = !(sigma(n+2) % eulerphi(n)); \\ Michel Marcus, Feb 05 2017

Extensions

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