Factorial is an operator ( ! ) and a function (FACTORIAL) that returns the factorial product of an integer.

Note: Twenty-factorial (20! or 2.432902e+18) is the largest factorial product that TDV natively supports. It is 9.223372e+18, which is within the range of BIGINT (-2**63 to +2**63 - 1). For maximum values in pushed functions, refer to the appropriate section of Function Support for Data Sources

Both of these return 120 (1 * 2 * 3 * 4 * 5).