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

Terms

a(0) =1a(1) =1a(2) =2a(3) =8a(4) =26a(5) =90a(6) =330a(7) =1240a(8) =4770a(9) =18701a(10) =74422a(11) =299890a(12) =1221226a(13) =5017930a(14) =20778462a(15) =86622414a(16) =363262562a(17) =1531406342a(18) =6486242016a(19) =27587989081a(20) =117785790794a(21) =504612883661