Can someone help me stop an arc4random generated number from appearing again?

Im using arc4random to generate a random number which im then using to display an image asset but i need a button that will stop arc4random generating that number again once its pressed

@IBAction func Button(_ sender: Any) {

    let BugRandom = arc4random_uniform(18)


    Smallbug.image = UIImage(named: "Bug\(BugRandom)")


}

Does anyone know if this is possible or what i should be looking for?