a(n) = [x^n] Product_{k>=2} ((1 + x^k)/(1 - x^k))^n.

Terms

a(0) =1a(1) =0a(2) =4a(3) =6a(4) =40a(5) =110a(6) =520a(7) =1778a(8) =7568a(9) =28320a(10) =116224a(11) =453046a(12) =1837600a(13) =7306234a(14) =29565848a(15) =118786526a(16) =481192480a(17) =1945153838a(18) =7895908852a(19) =32046260282a(20) =130370798320a(21) =530650047710