Expansion of e.g.f.: 2/(2-2*x-x^2).

Terms

a(0) =1a(1) =1a(2) =3a(3) =12a(4) =66a(5) =450a(6) =3690a(7) =35280a(8) =385560a(9) =4740120a(10) =64751400a(11) =972972000a(12) =15949256400a(13) =283232149200