G.f.: 1/(1-x-16*x^2).

Terms

a(0) =1a(1) =1a(2) =17a(3) =33a(4) =305a(5) =833a(6) =5713a(7) =19041a(8) =110449a(9) =415105a(10) =2182289a(11) =8823969a(12) =43740593a(13) =184924097a(14) =884773585a(15) =3843559137a(16) =17999936497a(17) =79496882689a(18) =367495866641