6.rb

#!/usr/bin/ruby -w
#
# Problem 6
# 14 December 2001
#
# The sum of the squares of the first ten natural numbers is,
#     1^2 + 2^2 + ... + 10^2 = 385
# The square of the sum of the first ten natural numbers is,
#     (1 + 2 + ... + 10)^2 = 552 = 3025
# Hence the difference between the sum of the squares of the first ten natural
# numbers and the square of the sum is 3025 - 385 = 2640.
#
# Find the difference between the sum of the squares of the first one hundred
# natural numbers and the square of the sum.

sum = squares = 0
1.upto(100) do |i|
  sum += i
  squares += i*i
end
puts sum*sum - squares