a(n) = n*F(n)*F(n+1), where F = A000045.

Terms

a(0) =0a(1) =1a(2) =4a(3) =18a(4) =60a(5) =200a(6) =624a(7) =1911a(8) =5712a(9) =16830a(10) =48950a(11) =140976a(12) =402624a(13) =1141933a(14) =3219580a(15) =9031050a(16) =25219824a(17) =70153016a(18) =194466672a(19) =537404835a(20) =1480993800a(21) =4071156726a(22) =11165970794a(23) =30561658848a(24) =83490220800a(25) =227687745625a(26) =619938027124