Project Euler Problem 6

module Enumerable
  def sum
    inject(0) {|a, n| a + n }
  end
end

def f(enum)
  sum1 = enum.map {|n| n ** 2 }.sum
  sum2 = enum.sum ** 2
  sum2 - sum1
end

p f(1 .. 10)
p f(1 .. 100)