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

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =6a(5) =17a(6) =48a(7) =144a(8) =449a(9) =1422a(10) =4568a(11) =14893a(12) =49139a(13) =163665a(14) =549570a(15) =1858754a(16) =6326343a(17) =21651064a(18) =74462327a(19) =257219221a(20) =892047965a(21) =3104749126a(22) =10841192392a(23) =37967942203a(24) =133333407639a(25) =469405472729