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

Terms

a(0) =1a(1) =1a(2) =3a(3) =6a(4) =16a(5) =38a(6) =110a(7) =276a(8) =818a(9) =2158a(10) =6528a(11) =17766a(12) =54622a(13) =151852a(14) =472674a(15) =1334886a(16) =4195328a(17) =11992486a(18) =37981982a(19) =109622228a(20) =349384626a(21) =1016304750a(22) =3256170672a(23) =9533400198a(24) =30680043630a(25) =90318157804a(26) =291763419458a(27) =862944630022