a(n) = n^2*(n+1)*(3*n+1)/4.

Terms

a(0) =0a(1) =2a(2) =21a(3) =90a(4) =260a(5) =600a(6) =1197a(7) =2156a(8) =3600a(9) =5670a(10) =8525a(11) =12342a(12) =17316a(13) =23660a(14) =31605a(15) =41400a(16) =53312a(17) =67626a(18) =84645a(19) =104690a(20) =128100a(21) =155232a(22) =186461a(23) =222180a(24) =262800a(25) =308750a(26) =360477a(27) =418446a(28) =483140a(29) =555060