Factorial
For example:. By agreement :. Also this equality is fulfilled in a natural way: The factorial is defined only for non-negative integers. The sequence of factorials of non-negative integers begins as follows: 1, 1, 2, 6, 24, 120, 720, 5040, 40 320, 362 880, 3 628 800, 39 916 800, 479 001 600, 6 227 020 800, 87 178 291 200, 1 307 674 368 000, 20 922 789 888 000, 355 687 428 096 000, 6 402 373 705 728 000, 121 645 100 408 832 000, 2 432 902 008 176 640 000, ... Factorials are often used in combinatorics, theory numbers and functional analysis. The factorial is an extremely fast growing function. It grows faster than a polynomial of any degree, and faster than an exponential function.