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

Terms

a(0) =0a(1) =0a(2) =3a(3) =19a(4) =66a(5) =170a(6) =365a(7) =693a(8) =1204a(9) =1956a(10) =3015a(11) =4455a(12) =6358a(13) =8814a(14) =11921a(15) =15785a(16) =20520a(17) =26248a(18) =33099a(19) =41211a(20) =50730a(21) =61810a(22) =74613a(23) =89309a(24) =106076a(25) =125100a(26) =146575a(27) =170703a(28) =197694a(29) =227766