Implementing a prime number counting algorithm

In this section, we are going to create an algorithm that will find all the prime numbers between zero to 2 million. Sound exciting? In traditional programming languages, this algorithm would need hundreds of lines of code, but in Ruby, we're going to see how to implement this efficiently.

To start, let's get access to the prime library, and to do this, use this code:

require 'prime' 

Next, store the prime numbers in an array with this code:

prime_array = Prime.take_while{ |p| p <2_000_000 } 

In this code, we created a variable called prime_array. In this variable, we store all the prime numbers up to 2 million.

Note

Ruby ignores underscores with integers, which is how we were able to represent the integer of 2 million with this syntax: 2_000_000. This is helpful when it comes to writing large numbers since we can use underscores instead of commas.

Before we go further, let's print prime_array to check whether it's working. If you execute the code...