a(n) = [x^n] Product_{k>=1} (1 + k*x^k)^n.

Terms

a(0) =1a(1) =1a(2) =5a(3) =28a(4) =137a(5) =726a(6) =3896a(7) =21071a(8) =115089a(9) =633007a(10) =3500740a(11) =19448573a(12) =108458924a(13) =606787572a(14) =3404112479a(15) =19142919543a(16) =107874784017a(17) =609021410570