Expansion of c(x(1+2x)), c(x) the g.f. of A000108.

Terms

a(0) =1a(1) =1a(2) =4a(3) =13a(4) =52a(5) =214a(6) =928a(7) =4141a(8) =18940a(9) =88258a(10) =417616a(11) =2001058a(12) =9690184a(13) =47348812a(14) =233158144a(15) =1155900541a(16) =5764510060a(17) =28898899594a(18) =145556001136a(19) =736206912982