login
This site is supported by donations to The OEIS Foundation.

 

Logo

Annual appeal: Please make a donation to keep the OEIS running! Over 6000 articles have referenced us, often saying "we discovered this result with the help of the OEIS".
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A077087 Numbers n such that sigma(n+1) = 3 * sigma(n). 3
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.

Sequence in context: A163863 A251917 A222928 * A179696 A249840 A061374

Adjacent sequences:  A077084 A077085 A077086 * A077088 A077089 A077090

KEYWORD

nonn

AUTHOR

Labos Elemer, Oct 31 2002

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified November 21 22:32 EST 2017. Contains 295054 sequences.