a(n) = 25*n*(n + 1)/2 + 3.

Terms

a(0) =3a(1) =28a(2) =78a(3) =153a(4) =253a(5) =378a(6) =528a(7) =703a(8) =903a(9) =1128a(10) =1378a(11) =1653a(12) =1953a(13) =2278a(14) =2628a(15) =3003a(16) =3403a(17) =3828a(18) =4278a(19) =4753a(20) =5253a(21) =5778a(22) =6328a(23) =6903a(24) =7503a(25) =8128a(26) =8778a(27) =9453a(28) =10153a(29) =10878