a(n) = n*(n-1)^4/2.

Terms

a(0) =0a(1) =0a(2) =1a(3) =24a(4) =162a(5) =640a(6) =1875a(7) =4536a(8) =9604a(9) =18432a(10) =32805a(11) =55000a(12) =87846a(13) =134784a(14) =199927a(15) =288120a(16) =405000a(17) =557056a(18) =751689a(19) =997272a(20) =1303210a(21) =1680000a(22) =2139291a(23) =2693944a(24) =3358092a(25) =4147200a(26) =5078125a(27) =6169176a(28) =7440174a(29) =8912512