[seqfan] Number of solutions of sigma(x) = n.

[Allan Wechsler]

If I have done this right, the first few entries are 1, 0, 1, 1, 0, 2, 1,
1, 0, 0. For example, a(6) = 2 because sigma(5) = sigma(6) = 6, and a(24) =
3 because sigma(14) = sigma(15) = sigma(23) = 24.

If my paper calculations were right for the first few entries, I am really
surprised to find this missing from OEIS, and am inclined to nominate it
for sequence A250000. It has many links with existing sequences relating to
sums of divisors.