Expansion of g.f.: (1+x+x^2)/(1-4*x-4*x^2).

Terms

a(0) =1a(1) =5a(2) =25a(3) =120a(4) =580a(5) =2800a(6) =13520a(7) =65280a(8) =315200a(9) =1521920a(10) =7348480a(11) =35481600a(12) =171320320a(13) =827207680a(14) =3994112000a(15) =19285278720a(16) =93117562880a(17) =449611366400