G.f. is the polynomial (Product_{k=1..23} (1 - x^(3*k)))/(1-x)^23.

Terms

a(0) =1a(1) =23a(2) =276a(3) =2299a(4) =14927a(5) =80454a(6) =374439a(7) =1545807a(8) =5771919a(9) =19781035a(10) =62936510a(11) =187603065a(12) =527817225a(13) =1410264780a(14) =3596907555a(15) =8795685646a(16) =20699124413a(17) =47031284166a(18) =103467710300a(19) =220946372920a(20) =458974273140a(21) =929305397041