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

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =1a(5) =5a(6) =1a(7) =13a(8) =2a(9) =33a(10) =1a(11) =90a(12) =1a(13) =193a(14) =55a(15) =450a(16) =1a(17) =1295a(18) =1a(19) =2321a(20) =1216a(21) =5121a(22) =1a(23) =16528a(24) =2a(25) =24577a(26) =20413a(27) =54529a(28) =1a(29) =193446