A110817 - OEIS

A110817

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

1, 2, 9, 135, 32895, 2147516415

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OFFSET

1,2

COMMENTS

These are all the terms up to 10^8.

LINKS

EXAMPLE

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

MATHEMATICA

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

CROSSREFS

KEYWORD

nonn

AUTHOR

Joseph L. Pe, Sep 15 2005

EXTENSIONS

a(6) from Donovan Johnson, Nov 15 2009

STATUS

approved