Expansion of g.f.: x*(1 - x)*(1 + x)/(1 - x - 9*x^2 - x^3 + x^4).

Terms

a(0) =0a(1) =1a(2) =1a(3) =9a(4) =19a(5) =100a(6) =279a(7) =1189a(8) =3781a(9) =14661a(10) =49600a(11) =184141a(12) =641421a(13) =2333629a(14) =8240959a(15) =29700900a(16) =105561739a(17) =378777169a(18) =1350292761a(19) =4835148121a(20) =17260998400a(21) =61748847081a(22) =220582688041a(23) =788748162049