It doesn’t say, but the numbers can be repeated. So the number 3 could be in the sequence twice.
It also doesn’t like you redo a level if you failed it. It would be nice to have the option of retrying it instead of it always populating a new sequence.
You get five lines to guess the code, it does use the yellow and green squares to let you know if it’s in the right place, or right number wrong place. Once you do the 5th guess you don’t have the option of retrying that sequence if you didn’t get it correct.
I believe it could be improved by allowing the player to choose if they will re try that sequence or get a new one. And tell the players when they first start the game that numbers can be repeated.