OFFSET
1,1
COMMENTS
The cases sigma(k) = 3*sigma(k+1) are rarer: k=180, 12000, 30996, 47940, ... [R. J. Mathar, Jul 25 2009]
LINKS
Donovan Johnson, Table of n, a(n) for n = 1..1000
MATHEMATICA
f[n_]:=DivisorSigma[1, n]; lst={}; Do[If[f[n]==f[n+1]*2, AppendTo[lst, n]], {n, 9!}]; lst
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Joseph Stephan Orlovsky, Jul 22 2009
EXTENSIONS
Edited by R. J. Mathar, Jul 25 2009
STATUS
approved