a(n) = (3*n+7)*(3*n+2)/2.

Terms

a(0) =7a(1) =25a(2) =52a(3) =88a(4) =133a(5) =187a(6) =250a(7) =322a(8) =403a(9) =493a(10) =592a(11) =700a(12) =817a(13) =943a(14) =1078a(15) =1222a(16) =1375a(17) =1537a(18) =1708a(19) =1888a(20) =2077a(21) =2275a(22) =2482a(23) =2698a(24) =2923a(25) =3157a(26) =3400a(27) =3652a(28) =3913a(29) =4183