E.g.f. cosh(x)/(1+x).

Terms

a(0) =1a(1) =-1a(2) =3a(3) =-9a(4) =37a(5) =-185a(6) =1111a(7) =-7777a(8) =62217a(9) =-559953a(10) =5599531a(11) =-61594841a(12) =739138093a(13) =-9608795209a(14) =134523132927