a(n) = [x^n] (1/(1 - x))*Product_{k>=1} (1 + x^k)^n.

Terms

a(0) =1a(1) =2a(2) =6a(3) =23a(4) =90a(5) =362a(6) =1491a(7) =6225a(8) =26242a(9) =111479a(10) =476466a(11) =2046464a(12) =8825559a(13) =38191467a(14) =165751529a(15) =721177328a(16) =3144703234a(17) =13739010855a(18) =60127642329a(19) =263545670385