Full explained I made a algorithm which can guess number only using "lesser than" or "greater than" in least step(you can download via sketchware[android app] named number finder). I started to wonder that how would the graph of "number" versus "step taken for guessing" look . Results are here. This algorithm is quite powerful , it can guess number in millions within 20-175 steps. I can't find any use of this algorithm but still fun to use ;)