G.f.: (1-4*x)^(-1/4) * (1-8*x)^(-1/8).

Terms

a(0) =1a(1) =2a(2) =8a(3) =40a(4) =228a(5) =1416a(6) =9312a(7) =63648a(8) =446760a(9) =3195728a(10) =23179840a(11) =169929280a(12) =1256234720a(13) =9350462400a(14) =69993150720a(15) =526455847680