euler-problem-12.rb

require 'prime'

def divisors_count(n)
  Prime.prime_division(n).reduce(1) do |mem, prime_factor|
    mem * (prime_factor[1] + 1)
  end
end

def triangle_number(n)
  (n)*(n+1)/2
end

i = 1
divs = 0
last_tn = 0
while divs < 500 do
  i += 1
  last_tn = triangle_number(i)
  divs = divisors_count(last_tn)
end
puts last_tn