a(n) = (8*n+1)*(8*n+7).

Terms

a(0) =7a(1) =135a(2) =391a(3) =775a(4) =1287a(5) =1927a(6) =2695a(7) =3591a(8) =4615a(9) =5767a(10) =7047a(11) =8455a(12) =9991a(13) =11655a(14) =13447a(15) =15367a(16) =17415a(17) =19591a(18) =21895a(19) =24327a(20) =26887a(21) =29575a(22) =32391a(23) =35335a(24) =38407a(25) =41607a(26) =44935a(27) =48391a(28) =51975a(29) =55687