G.f. satisfies: A(x) = Sum_{n>=0} x^n*(A(x)^n + A(-x)^n)/2.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =4a(5) =11a(6) =24a(7) =70a(8) =163a(9) =496a(10) =1199a(11) =3746a(12) =9291a(13) =29572a(14) =74712a(15) =241078a(16) =617612a(17) =2013979a(18) =5215990a(19) =17151362a(20) =44809646a(21) =148345585a(22) =390352720a(23) =1299558642a(24) =3440133086a(25) =11507046875a(26) =30615708092a(27) =102821083832a(28) =274759034372a(29) =925976586616