OFFSET
1,1
COMMENTS
Sequence seems to consist only of odd values.
LINKS
Harry J. Smith, Table of n, a(n) for n = 1..761
MATHEMATICA
f[n_]:=DivisorSigma[1, n]; lst={}; Do[If[2*f[n]==f[n+1], AppendTo[lst, n]], {n, 9!}]; lst (* Vladimir Joseph Stephan Orlovsky, Jul 22 2009 *)
Position[Partition[DivisorSigma[1, Range[300000]], 2, 1], _?(2#[[1]]==#[[2]]&), 1, Heads->False]//Flatten (* Harvey P. Dale, Oct 21 2024 *)
PROG
(PARI) isok(k) = { sigma(k+1) == 2*sigma(k) } \\ Harry J. Smith, May 08 2010
CROSSREFS
KEYWORD
nonn
AUTHOR
Benoit Cloitre, Feb 18 2002
EXTENSIONS
Terms added by Harry J. Smith, May 08 2010
STATUS
approved