a(n) = n*(n^2 - 6*n + 11)/6.

Terms

a(0) =0a(1) =1a(2) =1a(3) =1a(4) =2a(5) =5a(6) =11a(7) =21a(8) =36a(9) =57a(10) =85a(11) =121a(12) =166a(13) =221a(14) =287a(15) =365a(16) =456a(17) =561a(18) =681a(19) =817a(20) =970a(21) =1141a(22) =1331a(23) =1541a(24) =1772a(25) =2025a(26) =2301a(27) =2601a(28) =2926a(29) =3277