David W. Wilson schrieb: > Does there exist a non-square number which is square (mod 2^n) for every > n >= 0? > Call this non-square a0 and have a look at n0=ceil(log(a0)/log(2)). for every n>=n0: a0 == a0 mod 2^n and a0 has to be square and non-square simultaneously. cantradiction. P²