It’s quite another again to find the prime factors of a number fifty digits long. Though the best mathematicians have chewed on the problem for hundreds of years, there just doesn’t seem to be ...

So is the set of all numbers that have exactly two or three or 100 prime factors. Primitive sets were introduced by the mathematician Paul Erdős in the 1930s.

Find one million consecutive positive numbers, none of which are prime.

We have known for millennia that an infinite number of prime numbers, i.e., 2, 3, 5, 7, 11, etc., can be divided by themselves and the number 1 only.