OFFSET
1,1
EXAMPLE
Number 24 is in sequence because 24 = sigma(x) for composite numbers x = 14 and 15.
MATHEMATICA
nn = 600; t = Table[If[PrimeQ[n], -1, DivisorSigma[1, n]], {n, nn}]; t2 = Rest[Select[Sort[Tally[t]], #[[2]] > 1 &]]; Select[Transpose[t2][[1]], # <= nn &] (* T. D. Noe, Feb 13 2012 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Feb 07 2012
EXTENSIONS
Corrected by T. D. Noe, Feb 13 2012
STATUS
approved