E.g.f. 1/sqrt(1+2x+4x^2).

Terms

a(0) =1a(1) =-1a(2) =-1a(3) =21a(4) =-111a(5) =-345a(6) =14895a(7) =-143955a(8) =-760095a(9) =49774095a(10) =-699437025a(11) =-5221460475a(12) =458621111025