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

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =16a(5) =46a(6) =140a(7) =435a(8) =1382a(9) =4474a(10) =14687a(11) =48787a(12) =163703a(13) =554009a(14) =1888794a(15) =6481220a(16) =22366415a(17) =77575617a(18) =270277602a(19) =945480612a(20) =3319582632a(21) =11693824752a(22) =41318554495a(23) =146399071577a(24) =520042511448