So (ii) implies that anan +an−1an−1 +...+ak−1ak−1 +ak+1ak+1 +...+a0 has a
prime divisor p ≡ 3(mod 4). We shall prove that p does not divide a. Assume
that p divides a. Then p divides a0. So p = a0, since a0 is prime. Therefore b2
is multiple of p2, but anan + an−1an−1 + ... + a0 is not multiple of p2, because
a1 = 0. This is a contradiction to equation (2).