G.f. A(x) satisfies: A(x) = Product_{k>=1} (1 + k*x^k*A(x)).

Terms

a(0) =1a(1) =1a(2) =3a(3) =10a(4) =30a(5) =98a(6) =323a(7) =1083a(8) =3684a(9) =12710a(10) =44272a(11) =155608a(12) =551259a(13) =1965952a(14) =7052990a(15) =25436711a(16) =92168542a(17) =335376653a(18) =1224991077a(19) =4489818110a(20) =16507728007a(21) =60868469848a(22) =225030777305a(23) =833961333273