How do I create some random numbers without duplicate

I want to generate some numbers (for example 3 numbers from 30) which all have to be unique. for example every time you click on a sprite it generates a unique random number that is not the same each time you click on it.

I found this link (below) and tried to follow it, yet i got stuck somewhere on part 8 or 9 the example i could not replicate something so i gave up, the project was on dropbox so i can not download it so i could follow iot in construct 2

https://www.scirra.com/tutorials/315/ge ... duplicates

I am new so any help appreciated.

plugin-smart-random_t163624?&hilit=Smart+random

Thanks for your help blackhornet, that worked great