Find the difference between the sum of the squares and the square of the sums of the first N natural numbers.
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 = 55**2 = 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.
Problem 6 at Project Euler view source