G.f. A(x) satisfies A(x) = 1 + x*A(x) / (1 - x*A(x)^4).

Terms

a(0) =1a(1) =1a(2) =2a(3) =8a(4) =38a(5) =196a(6) =1073a(7) =6120a(8) =35968a(9) =216304a(10) =1324676a(11) =8232981a(12) =51796538a(13) =329229344a(14) =2111031444a(15) =13638557196a(16) =88695018723a(17) =580153216512