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The factorial of 4, which is written as , is . Similarly, . The number grows very quickly as increases. The double factorial of a number , which is written as , is an extension to the normal factorial. When is odd, . When is even, .
Contributed by: Ed Pegg Jr (March 2011)
Additional Contributions by: Rob Morris
Open content licensed under CC BY-NC-SA
Wolfram Demonstrations Project
Published: March 7 2011