Expansion of c(-x^2)(1+2x-sqrt(1+4x^2))/2, c(x) the g.f. of A000108.

Terms

a(0) =0a(1) =1a(2) =-1a(3) =-1a(4) =2a(5) =2a(6) =-5a(7) =-5a(8) =14a(9) =14a(10) =-42a(11) =-42a(12) =132a(13) =132a(14) =-429a(15) =-429a(16) =1430a(17) =1430a(18) =-4862a(19) =-4862a(20) =16796a(21) =16796a(22) =-58786a(23) =-58786a(24) =208012a(25) =208012a(26) =-742900a(27) =-742900a(28) =2674440a(29) =2674440