E.g.f. 2*sqrt(3)/3*arctan(sqrt(3)*x/(x+2)).

Terms

a(0) =1a(1) =-1a(2) =0a(3) =6a(4) =-24a(5) =0a(6) =720a(7) =-5040a(8) =0a(9) =362880a(10) =-3628800a(11) =0a(12) =479001600a(13) =-6227020800a(14) =0a(17) =0a(20) =0