Factorial

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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
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"Factorial"
http://demonstrations.wolfram.com/Factorial/
Wolfram Demonstrations Project
Published: March 7 2011