G.f.: Sum_{k>=0} x^(k*(k+1)/2) * Product_{j=1..k} ((1 + x^j)/(1 - x^j))^2.

Terms

a(0) =1a(1) =1a(2) =4a(3) =9a(4) =16a(5) =28a(6) =49a(7) =84a(8) =140a(9) =228a(10) =361a(11) =560a(12) =856a(13) =1288a(14) =1916a(15) =2821a(16) =4108a(17) =5928a(18) =8480a(19) =12024a(20) =16920a(21) =23637a(22) =32788a(23) =45196a(24) =61928a(25) =84368a(26) =114332a(27) =154160a(28) =206857a(29) =276308