# How to Use Ruby Prime

09/22/2021

Contents

## Using Ruby Prime

Ruby Prime is a built-in module that provides a number of methods for working with prime numbers. Here are some examples of how to use Ruby Prime:

### Checking if a number is prime

You can use the prime? method to check if a number is prime:

``````require 'prime'

puts Prime.prime?(17)  # true
puts Prime.prime?(21)  # false
``````

### Generating a list of prime numbers

You can use the each method to generate a list of prime numbers:

``````require 'prime'

Prime.each(20) do |prime|
puts prime
end
``````

This will print out all the prime numbers less than or equal to 20.

### Getting the nth prime number

You can use the first method to get the first n prime numbers:

``````require 'prime'

puts Prime.first(5)  # [2, 3, 5, 7, 11]
``````

### Generating a range of prime numbers

You can use the take_while method to generate a range of prime numbers:

``````require 'prime'

primes = Prime.take_while { |p| p < 20 }

puts primes.inspect  # [2, 3, 5, 7, 11, 13, 17, 19]
``````

This will generate all the prime numbers less than 20 and put them into an array.

### Generating prime factorization

You can use the prime_division method to get the prime factorization of a number:

``````require 'prime'

puts Prime.prime_division(28).inspect  # [[2, 2], [7, 1]]
``````

This will print out the prime factorization of 28, which is 2^2 * 7^1.