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

Terms

a(0) =1a(1) =2a(2) =13a(3) =80a(4) =538a(5) =3740a(6) =26650a(7) =193160a(8) =1417945a(9) =10511450a(10) =78533629a(11) =590485208a(12) =4463274232a(13) =33886781840a(14) =258260802232