Expansion of e.g.f. (1 + x * exp(x))^3.

Terms

a(0) =1a(1) =3a(2) =12a(3) =51a(4) =228a(5) =1035a(6) =4698a(7) =21063a(8) =92424a(9) =395091a(10) =1643790a(11) =6664383a(12) =26387100a(13) =102286587a(14) =389125506a(15) =1455994935a(16) =5368721808a(17) =19541252259a(18) =70312410774a(19) =250408115823a(20) =883617559140