Find all positive integers n, less than 17, for which n! is an integral multiple of 49.
Imagine writing down the definition of n! in full
1 x 2 x 3 x 4 x ... x n
if it has both 14 in it then it means it's a multiple of 49 because it has one 7 (in 7) and another 7 (in 14) as prime factors. So an an n must be at least 14.