G.f: exp( Sum_{n>=1} x^n/n * Product_{d|n} (1 + d*x^(n/d))^d ).

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =10a(5) =27a(6) =76a(7) =242a(8) =852a(9) =3016a(10) =11262a(11) =47004a(12) =204761a(13) =894673a(14) =4134909a(15) =20370101a(16) =101904474a(17) =521459464a(18) =2813783214a(19) =15616060213a(20) =87143803196a(21) =502477538546