a(n) = (11*n^2 - 7*n)/2.

Terms

a(0) =0a(1) =2a(2) =15a(3) =39a(4) =74a(5) =120a(6) =177a(7) =245a(8) =324a(9) =414a(10) =515a(11) =627a(12) =750a(13) =884a(14) =1029a(15) =1185a(16) =1352a(17) =1530a(18) =1719a(19) =1919a(20) =2130a(21) =2352a(22) =2585a(23) =2829a(24) =3084a(25) =3350a(26) =3627a(27) =3915a(28) =4214a(29) =4524