Prime multiplication table

gistfile1.rb

#!/usr/bin/env ruby
require 'open-uri'

how_many = ARGV.pop || 10
how_many = how_many.to_i

module Prime
  def self.take(count)
    search_space = 2..count**2
    search_space.select { |x| is_prime?(x) }.take(count)
  end

  def self.is_prime?(number)
    (2..(number**0.5).to_i).select { |divisor| number % divisor == 0 }.empty?
  end
end

first_row = [1] + Prime.take(how_many)
pad_to    = (first_row.last**2).to_s.size
comp      = first_row.flat_map { |x| first_row.map { |y| x*y } }.map { |z| (z==1 ? "" : z.to_s).rjust(pad_to) }

comp.each_slice(how_many + 1) do |line|
  puts line.join(" | ")
end