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

Terms

a(0) =1a(1) =1a(2) =3a(3) =13a(4) =61a(5) =310a(6) =1657a(7) =9190a(8) =52393a(9) =305155a(10) =1807922a(11) =10861507a(12) =66013637a(13) =405162518a(14) =2507635730a(15) =15633283370a(16) =98082119253a(17) =618809792699