gistfile1.rbx

def problem37
  #The number 3797 has an interesting property. Being prime itself, it is possible to 
  #continuously remove digits from left to right, and remain prime at each stage: 
  #3797, 797, 97, and 7. 
	#Similarly we can work from right to left: #3797, 379, 37, and 3.
	#primes = [37, 797, 3797]
	primes = []
	
	lefts = [2,3,5,7]
	rights = [3,7]
	middles = [1,3,7,9]

	lefts.each do |left|
		rights.each do |right|
			num = (left.to_s + right.to_s).to_i
			primes << num if is_prime_right(num) && is_prime_left(num)
			middles.each do |middle|
				num = (left.to_s + middle.to_s + right.to_s).to_i
				primes << num if is_prime_right(num) && is_prime_left(num)
				middles.each do |middle2|
					num = (left.to_s + middle.to_s + middle2.to_s + right.to_s).to_i
					primes << num if is_prime_right(num) && is_prime_left(num)
					middles.each do |middle3|
						num = (left.to_s + middle.to_s + middle2.to_s + middle3.to_s + right.to_s).to_i
						primes << num if is_prime_right(num) && is_prime_left(num)
						middles.each do |middle4|
							num = (left.to_s + middle.to_s + middle2.to_s + middle3.to_s + middle4.to_s + right.to_s).to_i
							primes << num if is_prime_right(num) && is_prime_left(num)
						end
					end
				end
			end
		end
	end

	puts "primes: #{primes.inspect} (#{primes.size})"
	puts "sum: #{primes.sum}"
  #so the numbers so far are 3797, 379, 797, 97, 37 (only 6 more to find)
end