G.f.: Product_{n>0} ((1+x^n)/(1-x^n))^n.

Terms

a(0) =1a(1) =2a(2) =6a(3) =16a(4) =38a(5) =88a(6) =196a(7) =420a(8) =878a(9) =1794a(10) =3584a(11) =7032a(12) =13572a(13) =25792a(14) =48352a(15) =89512a(16) =163774a(17) =296444a(18) =531234a(19) =943072a(20) =1659560a(21) =2896376a(22) =5015700a(23) =8622108a(24) =14718652a(25) =24960138a(26) =42062200a(27) =70458160a(28) =117349856a(29) =194381704