def factor(n)
  return 1 if n < 2
  2.upto(n - 1) do |k|
    return k if 0 == n % k
  end
  1
end



def prime?(n)
  1 == factor(n)
end



if __FILE__ == $0 && ARGV.size > 0

  open(ARGV.first) do |io|
    io.each_line do |line|
      n = line.strip.to_i
      puts "#{n} is a prime number" if prime?(n)
    end
  end

end