a(n) = [q^n] (1 - q)^n / Product_{j=1..n} (1 - q^j).

Terms

a(0) =1a(1) =0a(2) =1a(3) =-1a(4) =2a(5) =-4a(6) =9a(7) =-21a(8) =49a(9) =-112a(10) =249a(11) =-539a(12) =1143a(13) =-2396a(14) =5013a(15) =-10550a(16) =22420a(17) =-48086a(18) =103703a(19) =-223806a(20) =481388a(21) =-1029507a(22) =2187944a(23) =-4625058a(24) =9742223a(25) =-20490753a(26) =43111808a(27) =-90840465a(28) =191773014a(29) =-405523635