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

Terms

a(0) =1a(1) =2a(2) =3a(3) =5a(4) =5a(5) =12a(6) =7a(7) =32a(8) =10a(9) =90a(10) =11a(11) =264a(12) =13a(13) =686a(14) =105a(15) =1809a(16) =17a(17) =5166a(18) =19a(19) =11560a(20) =2856a(21) =28182a(22) =23a(23) =81456a(24) =26a(25) =159770a(26) =61263a(27) =375004a(28) =29a(29) =1122660