A015834 Numbers k such that phi(k) | sigma(k + 1).

1, 2, 4, 5, 6, 9, 10, 13, 14, 20, 21, 30, 32, 34, 43, 45, 54, 55, 65, 68, 70, 104, 109, 114, 129, 132, 140, 151, 153, 160, 176, 183, 203, 234, 245, 252, 279, 314, 340, 370, 407, 434, 441, 539, 550, 580, 589, 620, 635, 644, 741, 765, 798, 806, 845, 860, 883

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

PARI

is(n)=!(sigma(n+1)%eulerphi(n)) \\ Charles R Greathouse IV, Sep 25 2012

Extensions

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