Expansion of e.g.f. exp(3*x)*sech(x).

Terms

a(0) =1a(1) =3a(2) =8a(3) =18a(4) =32a(5) =48a(6) =128a(7) =528a(8) =512a(9) =-6912a(10) =2048a(11) =357888a(12) =8192a(13) =-22351872a(14) =32768a(15) =1903822848a(16) =131072a(17) =-209865080832a(18) =524288a(20) =2097152a(22) =8388608a(24) =33554432a(26) =134217728