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

Terms

a(0) =1a(1) =1a(2) =2a(3) =7a(4) =26a(5) =98a(6) =389a(7) =1617a(8) =6884a(9) =29818a(10) =131284a(11) =585966a(12) =2644084a(13) =12041541a(14) =55280357a(15) =255556439a(16) =1188632292a(17) =5558332388a(18) =26116960640a(19) =123243816854a(20) =583830832350