Riordan array (1/(1-4*x*c(x)),xc(x)), c(x) the g.f. of A000108.

Terms

a(0) =1a(1) =4a(2) =1a(3) =20a(4) =5a(5) =1a(6) =104a(7) =26a(8) =6a(9) =1a(10) =548a(11) =137a(12) =33a(13) =7a(14) =1a(15) =2904a(16) =726a(17) =178a(18) =41a(19) =8a(20) =1a(21) =15432a(22) =3858a(23) =954a(24) =228a(25) =50a(26) =9a(27) =1a(28) =82128a(29) =20532