Problem

The sum of the squares of the first ten natural numbers is,
1² + 2² + … + 10² = 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.

Solution

$sum1 = 0;
$sum2 = 0;
$diff = 0;

for ($i = 1; $i <= 100; $i++) {
  $sum1 += $i * $i;
  $sum2 += $i;
}

$sum2 = $sum2 * $sum2;
$diff = $sum2 - $sum1;

echo $diff;