a(n) = (8*n + 4)^2.

Terms

a(0) =16a(1) =144a(2) =400a(3) =784a(4) =1296a(5) =1936a(6) =2704a(7) =3600a(8) =4624a(9) =5776a(10) =7056a(11) =8464a(12) =10000a(13) =11664a(14) =13456a(15) =15376a(16) =17424a(17) =19600a(18) =21904a(19) =24336a(20) =26896a(21) =29584a(22) =32400a(23) =35344a(24) =38416a(25) =41616a(26) =44944a(27) =48400a(28) =51984a(29) =55696