a(n) = (9*n^3 + 5*n)/2.

Terms

a(0) =7a(1) =41a(2) =129a(3) =298a(4) =575a(5) =987a(6) =1561a(7) =2324a(8) =3303a(9) =4525a(10) =6017a(11) =7806a(12) =9919a(13) =12383a(14) =15225a(15) =18472a(16) =22151a(17) =26289a(18) =30913a(19) =36050a(20) =41727a(21) =47971a(22) =54809a(23) =62268a(24) =70375a(25) =79157a(26) =88641a(27) =98854a(28) =109823a(29) =121575