Determine the largest integer such that there exist monic quadratic polynomials with integer coefficients so that for all integers there exists some and such that .
Solution
The construction for can be achieved with the polynomials , and . First we consider what kinds of polynomials we can have. Let . is either an integer or half an integer. Let . If is an integer then hits the perfect squares , etc. If is half an integer, then let . Then hits the product of two consecutive integers, i.e. 0, , etc. Assume there is a construction for . In both of the cases above, the most a polynomial can hit out of 10 is 4, in the case. Thus must hit , and and hit 3 integers each, out of . The only ways we can hit 3 out of 7 consecutive integers is with the sequences or . The only way a works is if it hits 3,5, and 9, which doesn't work since 5 was hit by . Otherwise, is , which doesn't work as hits 3,4, and 7, and must hit 6,8, and 9, which is impossible. Thus no construction for exists.