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

Terms

a(0) =1a(1) =1a(2) =-1a(3) =-4a(4) =7a(5) =33a(6) =-68a(7) =-344a(8) =767a(9) =4035a(10) =-9425a(11) =-50832a(12) =122436a(13) =671804a(14) =-1653776a(15) =-9189488a(16) =22992655a(17) =129001239a(18) =-326863667a(19) =-1847900500a(20) =4729547023a(21) =26903463697a(22) =-69424933968a(23) =-396930961632