E.g.f. (1/cosh(x)+tanh(x))*(exp(2*x)-exp(-x))/3.

Terms

a(0) =0a(1) =1a(2) =3a(3) =3a(4) =3a(5) =11a(6) =63a(7) =43a(8) =-837a(9) =171a(10) =34023a(11) =683a(12) =-1800477a(13) =2731a(14) =132912783a(15) =10923a(16) =-12927652917a(17) =43691a(19) =174763a(21) =699051a(23) =2796203a(25) =11184811a(27) =44739243