G.f. satisfies A(x) = 1 / (1 - x^3*A(x)^3 * (1 + x)).

Terms

a(0) =1a(1) =0a(2) =0a(3) =1a(4) =1a(5) =0a(6) =4a(7) =8a(8) =4a(9) =22a(10) =66a(11) =66a(12) =162a(13) =560a(14) =840a(15) =1529a(16) =4985a(17) =9690a(18) =16774a(19) =47349a(20) =107229a(21) =195500a(22) =483000a(23) =1172724a(24) =2311516a(25) =5249556a(26) =12910716a(27) =27299992a(28) =59765400a(29) =144602352