a(n) = 5*n^2 + 10*n.

Terms

a(0) =15a(1) =40a(2) =75a(3) =120a(4) =175a(5) =240a(6) =315a(7) =400a(8) =495a(9) =600a(10) =715a(11) =840a(12) =975a(13) =1120a(14) =1275a(15) =1440a(16) =1615a(17) =1800a(18) =1995a(19) =2200a(20) =2415a(21) =2640a(22) =2875a(23) =3120a(24) =3375a(25) =3640a(26) =3915a(27) =4200a(28) =4495a(29) =4800