OFFSET
1,1
LINKS
Math Forum, Topic: Petaflop machine not required / n + sigma(n) [Broken link]
EXAMPLE
For the n-th term, the n solutions are
2 {1}
11 {4, 5}
95 {32, 39, 47}
3623 {1687, 1727, 1751, 1811}
2363 {1011, 1099, 1139, 1147, 1181}
6143 {2048, 2631, 2863, 2951, 2983, 3007}
21263 {9111, 10231, 10319, 10447, 10471, 10519, 10631}
89303 {38271, 41671, 42991, 43367, 44287, 44311, 44431, 44651}
MATHEMATICA
nn=1000000; t=Table[n+DivisorSigma[1, n], {n, nn}]; t2=Select[t, # <= 2*nn+1&]; ts=Sort[Tally[t2]]; u=Union[Transpose[ts][[2]]]; c=Complement[Range[Max[u]], u]; If[c != {}, u=Range[c[[1]]-1]]; Table[Select[ts, #[[2]] == n &, 1][[1, 1]], {n, u}]
CROSSREFS
KEYWORD
nonn
AUTHOR
J. M. Bergot, Feb 16 2011
EXTENSIONS
Corrected and extended by T. D. Noe, Feb 16 2011
a(13)-a(28) from Donovan Johnson, Feb 17 2011
STATUS
approved