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A077087 Numbers n such that sigma(n+1) = 3 * sigma(n). 5
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

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

EXAMPLE

n=1: sigma[2]/sigma[1]=3/1=3; n=9563231: sigma[n+1]/sigma[n]=31026240/10342080=3

MAPLE

A077087:=proc(q) local n;

for n from 1 to q do if sigma(n+1)=3*sigma(n) then print(n); fi; od; end:

A077087 (10^10); # Paolo P. Lava, Mar 25 2013

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 *)

CROSSREFS

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

Sequence in context: A251917 A222928 A309031 * A179696 A249840 A061374

Adjacent sequences:  A077084 A077085 A077086 * A077088 A077089 A077090

KEYWORD

nonn

AUTHOR

Labos Elemer, Oct 31 2002

STATUS

approved

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Last modified October 3 22:17 EDT 2022. Contains 357237 sequences. (Running on oeis4.)