G.f. A(x) satisfies A(x)+A(x)^2+A(x)^3 = (1-sqrt(1-4*x))/2.

Terms

a(0) =0a(1) =1a(2) =0a(3) =1a(4) =3a(5) =5a(6) =22a(7) =64a(8) =198a(9) =710a(10) =2332a(11) =8105a(12) =28665a(13) =100653a(14) =361104a(15) =1301180a(16) =4713267a(17) =17217021a(18) =63140534a(19) =232702261a(20) =861507251a(21) =3200666821a(22) =11933894310a(23) =44636509320a(24) =167427781950a(25) =629691033738