A015843 Numbers k such that phi(k) | sigma(k + 5).

1, 2, 6, 9, 10, 16, 18, 22, 28, 30, 33, 42, 64, 65, 71, 72, 82, 87, 90, 114, 130, 136, 156, 182, 198, 208, 215, 280, 294, 336, 380, 390, 403, 451, 616, 660, 683, 755, 777, 964, 990, 1168, 1260, 1267, 1330, 1342, 1348, 1480, 1638, 1744, 1953, 2025, 2074, 2088

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

PARI

isok(n) = !(sigma(n+5) % eulerphi(n)); \\ Michel Marcus, Feb 05 2017

Extensions

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