a(n) = 25*n^2 - 5.

Terms

a(0) =20a(1) =95a(2) =220a(3) =395a(4) =620a(5) =895a(6) =1220a(7) =1595a(8) =2020a(9) =2495a(10) =3020a(11) =3595a(12) =4220a(13) =4895a(14) =5620a(15) =6395a(16) =7220a(17) =8095a(18) =9020a(19) =9995a(20) =11020a(21) =12095a(22) =13220a(23) =14395a(24) =15620a(25) =16895a(26) =18220a(27) =19595a(28) =21020a(29) =22495