Primality test in Ruby

bespoke.rb

def prime?(n)
  return false if n <= 1

  i = 2
  while i * i <= n
    return false if n % i == 0
    i += 1
  end
  true
end

prime? 0 # => false
prime? 1 # => false
prime? 2 # => true
prime? 3 # => true
prime? 4 # => false

stdlib.rb

require "prime"

0.prime? # => false
1.prime? # => false
2.prime? # => true
3.prime? # => true
4.prime? # => false