Not seeding the RNG is equivalent to a seed of 1.

defaultrandseed.go

package main

import (
	"fmt"
	"math/rand"
)

func show5(f func() int) {
	for i := 0; i < 5; i++ {
		fmt.Println(f())
	}
	fmt.Println()
}

func main() {
	show5(rand.Int)
	show5(rand.New(rand.NewSource(1)).Int)
}