Why sage wouldn give me polynomial representation of GF(8), but not GF(7)?
sage: G = GF(8, 'x')
sage: G.list()
[0, x, x^2, x + 1, x^2 + x, x^2 + x + 1, x^2 + 1, 1]
sage: G = GF(7, 'x')
sage: G.list()
[0, 1, 2, 3, 4, 5, 6]
Maybe there's no such thing as polynomial represenation of GF(7)?