OFFSET
1,2
FORMULA
A000005(a(n)) = n for a(n) > 0.
12 = max n such that a(n) > 0, a(n) = 0 for n > 12.
MATHEMATICA
With[{ds=Reverse[Table[{n, DivisorSigma[0, n]}, {n, 10, 99}]]}, Table[ SelectFirst[ ds, #[[2]]==k&], {k, 50}]][[All, 1]]/."NotFound"->0 (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, May 24 2019 *)
CROSSREFS
KEYWORD
nonn,base,less
AUTHOR
Jaroslav Krizek, Nov 27 2010
STATUS
approved