. * * To disable strict typing, comment out the directive below. */ declare(strict_types=1); function squareOfSum(int $max): int { $res = $max * ($max + 1) / 2; return $res * $res; } function sumOfSquares(int $max): int { $sum = 0; for ($i = 1; $i <= $max; $i++) { $sum += $i * $i; } return $sum; } function difference(int $max): int { return squareOfSum($max) - sumOfSquares($max); }