a(n) = Sum_{d|n} d^(n-d+1).

Terms

a(0) =1a(1) =3a(2) =4a(3) =13a(4) =6a(5) =120a(6) =8a(7) =1161a(8) =2197a(9) =16148a(10) =12a(11) =603190a(12) =14a(13) =5773008a(14) =50422464a(15) =201359377a(16) =18a(17) =16590656229a(18) =20a(19) =269768284118a(22) =24a(28) =30a(30) =32