a(n) = n*(n - 1)*(2*n^2 + n + 2)/6.

Terms

a(0) =0a(1) =0a(2) =4a(3) =23a(4) =76a(5) =190a(6) =400a(7) =749a(8) =1288a(9) =2076a(10) =3180a(11) =4675a(12) =6644a(13) =9178a(14) =12376a(15) =16345a(16) =21200a(17) =27064a(18) =34068a(19) =42351a(20) =52060a(21) =63350a(22) =76384a(23) =91333a(24) =108376a(25) =127700a(26) =149500a(27) =173979a(28) =201348a(29) =231826