Expansion of e.g.f. (1 + x + x^2)^x.

Terms

a(0) =1a(1) =0a(2) =2a(3) =3a(4) =-4a(5) =90a(6) =-126a(7) =-840a(8) =21104a(9) =-137592a(10) =-88920a(11) =15741000a(12) =-197234808a(13) =535289040a(14) =25582565904a(15) =-522317151720