Riordan array (1, x*c(3x)), c(x) the g.f. of A000108.

Terms

a(0) =1a(1) =0a(2) =1a(3) =0a(4) =3a(5) =1a(6) =0a(7) =18a(8) =6a(9) =1a(10) =0a(11) =135a(12) =45a(13) =9a(14) =1a(15) =0a(16) =1134a(17) =378a(18) =81a(19) =12a(20) =1a(21) =0a(22) =10206a(23) =3402a(24) =756a(25) =126a(26) =15a(27) =1a(28) =0a(29) =96228