The double exclamation mark is the symbol of factorial in mathematics. Like n! Represents the product of all natural numbers from 1 to n. This definition is often used in combinatorial mathematics, discrete mathematics and probability statistics. Factorial function refers to the factorial of natural number n, which plays an important role in calculating permutation and combination problems and numerical calculation.

Factorial function has many important properties. First, the factorial of zero is equal to1; Second, negative integers have no factorial. The growth rate of factorial function is also very fast, such as 24! The value of has exceeded10 2. In computer science, factorial function is a part of common algorithm, so it is a very important concept for developers and researchers.

The double exclamation mark symbol is not only used in mathematics, but also in programming languages. In some programming languages, double exclamation marks can represent NOT operators, that is, negation operations. In addition, it is also used in regular expressions to match characters of any length in a string. Therefore, in programming, we also need to pay attention to the usage and significance of the double exclamation mark symbol.