How many prime numbers are there between 50 and 70?

To understand why there are four prime numbers in this range, we first need to remember the definition of a prime. A prime number is a whole number greater than 1 that can only be divided evenly by 1 and itself. When we examine the integers from 50 to 70, we can immediately eliminate all the even numbers, as they are divisible by 2. We can also cross out any numbers ending in 5, since they are divisible by 5. This leaves us with a smaller list of candidates. From there, we test the remaining numbers, like 51 (divisible by 3 and 17) and 57 (divisible by 3 and 19), until only the true primes remain.

The four numbers that pass this test—53, 59, 61, and 67—are part of an infinite sequence of primes that has fascinated mathematicians for centuries. While the ancient Greek mathematician Euclid proved that there is no "last" prime number, they do become less frequent as numbers get larger. This particular set is also interesting because it contains a pair of "twin primes": 59 and 61. Twin primes are pairs of prime numbers that are separated by only one other number. Finding these special numbers is like a mathematical treasure hunt, and they serve as the fundamental building blocks for all other whole numbers.