G.f. A(x) satisfies: A(x)^2 = A(x^2) + 4*x.

Terms

a(0) =1a(1) =2a(2) =-1a(3) =2a(4) =-5a(5) =12a(6) =-30a(7) =82a(8) =-233a(9) =668a(10) =-1949a(11) =5802a(12) =-17503a(13) =53302a(14) =-163783a(15) =507418a(16) =-1582869a(17) =4966790a(18) =-15667573a(19) =49658264a(20) =-158059506a(21) =505013014a(22) =-1619144976a(23) =5207596574a(24) =-16797286048a(25) =54323516786a(26) =-176113786590a(27) =572236347200