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

Terms

a(0) =1a(1) =0a(2) =1a(3) =3a(4) =7a(5) =25a(6) =82a(7) =278a(8) =992a(9) =3552a(10) =12985a(11) =48107a(12) =179977a(13) =680079a(14) =2589915a(15) =9931573a(16) =38319117a(17) =148640195a(18) =579349123a(19) =2267818509a(20) =8911575579a(21) =35141656433a(22) =139018921717a(23) =551557089103