A110817 Numbers k such that (1/k)*sigma(k+1) is an integer.

1, 2, 9, 135, 32895, 2147516415

Offset

1,2

Comments

These are all the terms up to 10^8.

Links

Table of n, a(n) for n=1..6.

Example

sigma(2+1)/2 = 2, so 2 is a term of the sequence.

Mathematica

Select[Range[10^6], IntegerQ[DivisorSigma[1, # + 1]/# ] &]

Crossrefs

Sequence in context: A295331 A064448 A173215 * A189428 A110860 A370556

Adjacent sequences: A110814 A110815 A110816 * A110818 A110819 A110820

Keyword

nonn

Author

Joseph L. Pe, Sep 15 2005

Extensions

a(6) from Donovan Johnson, Nov 15 2009

Status

approved