G.f. satisfies: A(x) = (1 + x + x^2)^7 * A(x^2)^4.

Terms

a(0) =1a(1) =7a(2) =56a(3) =273a(4) =1463a(5) =6048a(6) =26537a(7) =97903a(8) =377384a(9) =1281497a(10) =4502463a(11) =14322560a(12) =46849089a(13) =141332583a(14) =436556440a(15) =1259742225a(16) =3710541975a(17) =10308494560a(18) =29165172617a(19) =78396244591a(20) =214217633672a(21) =559335671353