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factorial

mathrecursionbeginner

Calculates the factorial of a number.

Use recursion. If $n is less then or equal to 1, return 1. Otherwise, return the product of $n and the factorial of $n -1. Throws an exception if $n is a negative number.

function factorial($n)
{
  if ($n <= 1) {
    return 1;
  }

  return $n * factorial($n - 1);
}