Math-y challenge from http://www.zerocater.com/challenge/, find length of sequence of primes where the sum of the N-1 elements is divisible by the Nth element.

clean_prime_chain.rb

require 'prime'

prime_tester = Prime.instance
n = 3
sum = 2
len = 1

loop do
  if prime_tester.prime? n
    len = len + 1

    if sum % n == 0 and len > (ARGV[0].to_i || 3)
      break
    else
      sum = sum + n
    end
  end

  n = n + 1
end

# p nums.reduce(:+)
# p nums
p len