G.f.: Sum_{k>=0} (1 + k*x)^k * x^(3*k).

Terms

a(0) =1a(1) =0a(2) =0a(3) =1a(4) =1a(5) =0a(6) =1a(7) =4a(8) =4a(9) =1a(10) =9a(11) =27a(12) =28a(13) =16a(14) =96a(15) =257a(16) =281a(17) =250a(18) =1251a(19) =3161a(20) =3665a(21) =4321a(22) =19489a(23) =47685a(24) =58662a(25) =84099a(26) =354739a(27) =852216a(28) =1110344a(29) =1837924