class Integer

# File lib/multiply_prime_numbers_table/prime.rb, line 3
def is_prime?
  # Avoid to check number if is negative, is 1 or is EVEN distinct of 2
  return false if self <= 1 || (self.even? && self > 2)

  # returns false if the module dividing num by other number from 2 to the square root of itsel is zero
  2.upto(Math.sqrt(self).to_i) do |integer|
    return false if (self % integer).zero?
  end
  # if none of the previous checks match it means it's a prime number
  true
end