a(n) = 70*n^2 - 1.

Terms

a(0) =69a(1) =279a(2) =629a(3) =1119a(4) =1749a(5) =2519a(6) =3429a(7) =4479a(8) =5669a(9) =6999a(10) =8469a(11) =10079a(12) =11829a(13) =13719a(14) =15749a(15) =17919a(16) =20229a(17) =22679a(18) =25269a(19) =27999a(20) =30869a(21) =33879a(22) =37029a(23) =40319a(24) =43749a(25) =47319a(26) =51029a(27) =54879a(28) =58869a(29) =62999