Series reversion of (sqrt(1+4*x) - 1)/2 - x^2.

Terms

a(0) =1a(1) =2a(2) =6a(3) =25a(4) =114a(5) =560a(6) =2880a(7) =15321a(8) =83600a(9) =465322a(10) =2631668a(11) =15079922a(12) =87362184a(13) =510837760a(14) =3010987912a(15) =17870854206a(16) =106713713826a(17) =640659094566