G.f.: x^2 * f''(x), where f(x) = Product_{k>=1} 1 / (1 - x^k).

Terms

a(0) =0a(1) =0a(2) =4a(3) =18a(4) =60a(5) =140a(6) =330a(7) =630a(8) =1232a(9) =2160a(10) =3780a(11) =6160a(12) =10164a(13) =15756a(14) =24570a(15) =36960a(16) =55440a(17) =80784a(18) =117810a(19) =167580a(20) =238260a(21) =332640a(22) =462924a(23) =635030a(24) =869400a(25) =1174800a(26) =1583400a(27) =2113020a(28) =2810808a(29) =3706780