#!/usr/bin/ruby

def is_prime(n)
	if n <= 2
		return true
	elsif n.modulo(2) == 0
		return false
	else
		3.step(Math.sqrt(n).ceil, 2) do |i|
			if n.modulo(i) == 0
				return false
			end
		end
		return true
	end
end

if ARGV.length < 1
	puts "Usage: isprime number [number...]"
else
	ARGV.each do |n|
		if n.to_i < 1
			puts "Negative numbers and 0 not allowed."
			exit
		elsif is_prime(n.to_i)
			puts n.to_s + " is prime"
		else
			puts n.to_s + " is not prime"
		end
	end
end