A077087 Numbers k such that sigma(k+1) = 3 * sigma(k).

1, 1919, 2759, 11219, 27089, 50039, 58463, 100127, 113831, 115289, 120203, 131879, 148511, 233729, 244319, 308039, 461099, 554063, 596447, 1406303, 1486619, 2285519, 2880989, 5138783, 5369111, 5521619, 5736743, 6621383, 7496279, 7683191, 8571527, 8848619

Offset: 1

Author

Labos Elemer, Oct 31 2002

Keywords

• nonn

Examples

			k = 1: sigma(2)/sigma(1) = 3/1 = 3;
k = 9563231: sigma(k+1)/sigma(k) = 31026240/10342080 = 3.
		

Links

• Donovan Johnson, Table of n, a(n) for n = 1..500

Crossrefs

Cf. A000203, A002961, A067081, A077086, A272027 (3*sigma(n)).

Programs

Mathematica

Do[s=Mod[a=DivisorSigma[1, n+1], b=DivisorSigma[1, n]]; If[Equal[s, 0]&&Equal[a/b, 3], Print[n]], {n, 1, 10000000}]
Position[Partition[DivisorSigma[1,Range[9*10^6]],2,1],?(3#[[1]] == #[[2]]&),1,Heads->False]//Flatten (* _Harvey P. Dale, Oct 03 2017 *)