The notation "(n-1)!" represents the factorial of the number (n-1). Factorial, denoted by the exclamation mark, is a mathematical operation that multiplies a series of descending positive integers. For example, if n is 5, then (n-1) is 4, and 4! equals 4 × 3 × 2 × 1, which equals 24. Factorials are commonly used in various fields, including combinatorics, probability, and statistics. They help calculate permutations and combinations, which are essential for determining the number of ways to arrange or select items. Understanding factorials is crucial for solving many mathematical problems.