Here are 7 less common factorials that you probably didn't know: double factorial, subfactorial, primorial, super factorial, exponential factorial, hyper factorial

0:00 new factorials?
0:53 double factorial
see    • double factorial vs. regular factorial  
3:11 subfactorial
see    • subfactorial & derangement, an explic...  
5:33 primorial
7:13 super factorial by Sloane
8:38 super factorial by Pickover
10:22 exponential factorial
11:28 hyper factorial
see    • Hyperfactorial introduction  

Reference: https://en.wikipedia.org/wiki/Factorial

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