a(n) = 56*n^2 - 1.

Terms

a(0) =55a(1) =223a(2) =503a(3) =895a(4) =1399a(5) =2015a(6) =2743a(7) =3583a(8) =4535a(9) =5599a(10) =6775a(11) =8063a(12) =9463a(13) =10975a(14) =12599a(15) =14335a(16) =16183a(17) =18143a(18) =20215a(19) =22399a(20) =24695a(21) =27103a(22) =29623a(23) =32255a(24) =34999a(25) =37855a(26) =40823a(27) =43903a(28) =47095a(29) =50399