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

Terms

a(0) =0a(1) =0a(2) =2a(3) =12a(4) =40a(5) =100a(6) =210a(7) =392a(8) =672a(9) =1080a(10) =1650a(11) =2420a(12) =3432a(13) =4732a(14) =6370a(15) =8400a(16) =10880a(17) =13872a(18) =17442a(19) =21660a(20) =26600a(21) =32340a(22) =38962a(23) =46552a(24) =55200a(25) =65000a(26) =76050a(27) =88452a(28) =102312a(29) =117740