A015814 Numbers k such that phi(k + 1) divides sigma(k).

1, 3, 5, 6, 7, 11, 14, 15, 17, 23, 24, 28, 31, 33, 35, 47, 51, 53, 54, 55, 69, 71, 77, 87, 94, 107, 110, 127, 155, 170, 174, 191, 195, 209, 254, 261, 265, 285, 315, 322, 383, 385, 395, 399, 406, 423, 429, 431, 510, 564, 609, 636, 644, 647, 649, 672, 713

Offset: 1

Author

Robert G. Wilson v

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000010, A000203, A015834, A020492.

Programs

Mathematica

Select[Range[1000], Divisible[DivisorSigma[1, #], EulerPhi[1 + #]] &] (* David Nacin, Mar 01 2012 *)

PARI

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

Extensions

Definition corrected by David Nacin, Mar 01 2012