#!/bin/bash
ftrl(){  #factorial function
	declare -i arg  #argument to function ftrl
	declare -i iv   #intermediate values. 1, 2, 6, ...
	if [ $1 -le 1 ]
	then
		return 1
	else  #Compute n*f(n-1)
		let "arg=$1 - 1"  #n-1
		ftrl $arg         #f(n-1) , result stored in $?
		let "iv=$1 * $?"  #n*f(n-1)
		return $iv
	fi
}
ftrl $1
echo $?