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

Terms

a(0) =1a(1) =2a(2) =2a(3) =6a(4) =2a(5) =45a(6) =2a(7) =322a(8) =731a(9) =3383a(10) =2a(11) =132901a(12) =2a(13) =827641a(14) =10297068a(15) =33570818a(16) =2a(17) =2578617270a(18) =2a(19) =44812807567a(20) =678610493340a(21) =285312719189a(22) =2a(28) =2a(30) =2