a(n) = Sum_{d|n} d^(n-d) * binomial(d+n/d-2, d-1).

Terms

a(0) =1a(1) =2a(2) =2a(3) =10a(4) =2a(5) =131a(6) =2a(7) =1282a(8) =4376a(9) =16907a(10) =2a(11) =1138272a(12) =2a(13) =5793475a(14) =154455992a(15) =469893122a(16) =2a(17) =49501130330a(18) =2a(22) =2a(28) =2