5 Jul
2003
5 Jul
'03
6:27 p.m.
Is it not the case that a number appears in the N x N multiplication table precisely when none of its prime factors exceed N, and the number itself does not exceed N^2?
If N = 8 then 54 = 9*6 is not in the NxN multiplication table, yet 54 < N^2 and its prime factors are 2 and 3, both < N.