a(n) = (n/2) * (n^3 - 2*n^2 - 2*n + 5).

Terms

a(0) =0a(1) =1a(2) =1a(3) =12a(4) =58a(5) =175a(6) =411a(7) =826a(8) =1492a(9) =2493a(10) =3925a(11) =5896a(12) =8526a(13) =11947a(14) =16303a(15) =21750a(16) =28456a(17) =36601a(18) =46377a(19) =57988a(20) =71650a(21) =87591a(22) =106051a(23) =127282a(24) =151548a(25) =179125a(26) =210301a(27) =245376a(28) =284662a(29) =328483