a(n) = 14*n^2 - 1.

Terms

a(0) =13a(1) =55a(2) =125a(3) =223a(4) =349a(5) =503a(6) =685a(7) =895a(8) =1133a(9) =1399a(10) =1693a(11) =2015a(12) =2365a(13) =2743a(14) =3149a(15) =3583a(16) =4045a(17) =4535a(18) =5053a(19) =5599a(20) =6173a(21) =6775a(22) =7405a(23) =8063a(24) =8749a(25) =9463a(26) =10205a(27) =10975a(28) =11773a(29) =12599