a(n) = 68*n^2 - 1.

Terms

a(0) =67a(1) =271a(2) =611a(3) =1087a(4) =1699a(5) =2447a(6) =3331a(7) =4351a(8) =5507a(9) =6799a(10) =8227a(11) =9791a(12) =11491a(13) =13327a(14) =15299a(15) =17407a(16) =19651a(17) =22031a(18) =24547a(19) =27199a(20) =29987a(21) =32911a(22) =35971a(23) =39167a(24) =42499a(25) =45967a(26) =49571a(27) =53311a(28) =57187a(29) =61199