A072611 Numbers k such that phi(k) divides sigma(k+1) - sigma(k).

1, 2, 6, 14, 30, 40, 70, 140, 170, 174, 206, 215, 238, 390, 459, 518, 923, 957, 1334, 1364, 1540, 1634, 2685, 2974, 4364, 5180, 5934, 6048, 6467, 6510, 6623, 8028, 8094, 8260, 8814, 12136, 12954, 14099, 14841, 15416, 16472, 17094, 17835, 17927, 18873

Offset: 1

Author

Benoit Cloitre, Aug 07 2002

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A000010, A053222.

Programs

Mathematica

Select[Range[20000],Divisible[DivisorSigma[1,#+1]-DivisorSigma[1,#], EulerPhi[#]]&] (* Harvey P. Dale, Sep 15 2011 *)

Formula

Conjecture : Limit_{n -> infinity} log(a(n))/log(n) exists and = 2.6... .