Golang program to generate number of slices permutations of number entered by user

package main
 
import (
    "fmt"
    "os"
    "strconv"
)
 
func rangeSlice(start, stop int) []int {
    if start > stop {
        panic("Slice ends before it started")
    }
    xs := make([]int, stop-start)
    for i := 0; i < len(xs); i++ {
        xs[i] = i + 1 + start
    }
    return xs
}
 
func permutation(xs []int) (permuts [][]int) {
    var rc func([]int, int)
    rc = func(a []int, k int) {
        if k == len(a) {
            permuts = append(permuts, append([]int{}, a...))
        } else {
            for i := k; i < len(xs); i++ {
                a[k], a[i] = a[i], a[k]
                rc(a, k+1)
                a[k], a[i] = a[i], a[k]
            }
        }
    }
    rc(xs, 0)
 
    return permuts
}
 
func main() {
    if len(os.Args) < 2 {
        fmt.Println("Error: Add 1 numeric value ex. go run permutation.go 2")
        os.Exit(1)
    }
    num, err := strconv.Atoi(os.Args[1])
    if err != nil {
        fmt.Println(err.Error())
        os.Exit(1)
    }
 
    noOfPerms := permutation(rangeSlice(0, num))
    fmt.Println("Number of Permutation:",len(noOfPerms))
    for i := 0; i < len(noOfPerms); i++ {
        fmt.Println(noOfPerms[i])
    }
}