A056097 Numbers n such that phi(n) + 1 | sigma(n).

6, 8, 30, 36, 44, 156, 696, 944, 2800, 2928, 3600, 6660, 16064, 195456, 260864, 784128, 4189184, 12573696, 201289728, 17179541504, 274876596224, 824631361536

Offset: 1

Author

Robert G. Wilson v, Jul 27 2000

Keywords

• nonn

Comments

Contains 2^k(2^(k+2)-5) where 2^(k+2)-5 is prime; contains 2^k*3*(2^(k+2)-3) where 2^(k+2)-3 is prime; complete up to 5000000000. - David W. Wilson, May 16 2001

a(23) > 10^12. - Donovan Johnson, Feb 29 2012

Programs

Mathematica

Do[If[Mod[DivisorSigma[1, n], EulerPhi[n]+1]==0, Print[n]], {n, 1, 10^7}]

Extensions

a(20)-a(22) from Donovan Johnson, Feb 29 2012