a(n) = (8*n + 7)^2.

Terms

a(0) =49a(1) =225a(2) =529a(3) =961a(4) =1521a(5) =2209a(6) =3025a(7) =3969a(8) =5041a(9) =6241a(10) =7569a(11) =9025a(12) =10609a(13) =12321a(14) =14161a(15) =16129a(16) =18225a(17) =20449a(18) =22801a(19) =25281a(20) =27889a(21) =30625a(22) =33489a(23) =36481a(24) =39601a(25) =42849a(26) =46225a(27) =49729a(28) =53361a(29) =57121