G.f.: (2*x)/((1-(1-8*x)^(1/4))*(1-8*x)^(3/4)).

Terms

a(0) =1a(1) =3a(2) =19a(3) =132a(4) =955a(5) =7068a(6) =53074a(7) =402552a(8) =3075747a(9) =23632620a(10) =182384774a(11) =1412575112a(12) =10972566670a(13) =85442073304a(14) =666717107460