Calculate factorial number with Bash

#!/bin/bash
# Bash is not a good tool for large number calculation.
# Consider Python or Ruby

function fac {
    if [ $1 -le 1 ]; then
    echo 1
    return
    else
    echo $(( $( fac $(( $1 - 1 )) ) * $1 ))
    fi
}

fac 1
fac 10
fac 20
fac 50  # error
fac 100 # error