G.f. is the polynomial (Product_{k=1..17} (1 - x^(3*k)))/(1-x)^17.

Terms

a(0) =1a(1) =17a(2) =153a(3) =968a(4) =4828a(5) =20196a(6) =73643a(7) =240295a(8) =714969a(9) =1967393a(10) =5061733a(11) =12282075a(12) =28304167a(13) =62307023a(14) =131649309a(15) =268075466a(16) =527904757a(17) =1008342693a(18) =1873000449a(19) =3390989490a(20) =5995666674a(21) =10371347659a(22) =17579210264a(23) =29237321394a(24) =47774409494