Expansion of c(x*c(x)), where c(x) is the g.f. for A000108.

Terms

a(0) =1a(1) =1a(2) =3a(3) =11a(4) =44a(5) =185a(6) =804a(7) =3579a(8) =16229a(9) =74690a(10) =347984a(11) =1638169a(12) =7780876a(13) =37245028a(14) =179503340a(15) =870374211a(16) =4243141332a(17) =20786340271a(18) =102275718924a(19) =505235129250