The ABC conjecture of Masser and Oesterlé states that if (a, b, c) are coprime integers with a+ b+ c = 0, then sup(|a|, |b|, |c|) < cǫ(rad(abc)) 1+ǫ for any ǫ > 0. In [2], Oesterlé observes that if the ABC conjecture holds for all (a, b, c) with 16|abc, then the full ABC conjecture holds. We extend that result to show that, for every integer N , the “congruence ABC conjecture” that ABC holds fo...