User blog:Alejandro Magno/A Little Factorial Extension

n!! = (((...(((n!)!)!)...)!)!)!)! with n levels

n!!! = (((...(((n!!)!!)!!)...)!!)!!)!!)!! with n levels

n!!!...!!! = (((...(((n!!!..!!)!!!...!!)!!!...!!)...)!!!...!!)!!!...!!)!!!...!!)!!!...!! with n levels

n!_2 = n!!!...!!! with n !'s

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