A prime number is that which is measured by a unit alone (Euclid).

A prime number is a number with only two factors, itself and one.

A prime number is only divisible by itself and one.

A prime number cannot be produced by any two numbers (not including itself).

The first few primes are: {2, 3, 5, 7, 11, 13, 17, 19, 23, …}

Notice there are numbers missing in the above set if we expect to count in order (1, 2, 3, 4…). This is because all those missing numbers are some combination of the primes. …