a(n) = n^4*(n+1)^4/8.

Terms

a(0) =2a(1) =162a(2) =2592a(3) =20000a(4) =101250a(5) =388962a(6) =1229312a(7) =3359232a(8) =8201250a(9) =18301250a(10) =37949472a(11) =74030112a(12) =137149922a(13) =243101250a(14) =414720000a(15) =684204032a(16) =1095962562a(17) =1710072162a(18) =2606420000a(19) =3889620000a(20) =5694792642a(21) =8194304162a(22) =11605565952a(23) =16200000000a(24) =22313281250a(25) =30356972802