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A110817
Numbers k such that (1/k)*sigma(k+1) is an integer.
1
1, 2, 9, 135, 32895, 2147516415
OFFSET
1,2
COMMENTS
These are all the terms up to 10^8.
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: A064448 A376925 A173215 * A189428 A110860 A370556
KEYWORD
nonn
AUTHOR
Joseph L. Pe, Sep 15 2005
EXTENSIONS
a(6) from Donovan Johnson, Nov 15 2009
STATUS
approved