G.f.: Sum_{n>=0} Product_{k=1..n} Series_Reversion( x*(1 - x^k) ).

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =10a(5) =25a(6) =73a(7) =214a(8) =679a(9) =2189a(10) =7331a(11) =24867a(12) =86269a(13) =302144a(14) =1072621a(15) =3837768a(16) =13853674a(17) =50319789a(18) =183941789a(19) =675731105a(20) =2494370326a(21) =9244865453a(22) =34394851701a(23) =128390336942a(24) =480749791772