Sandbox
RNGdle Sandbox
Enter a number from 0 to 999,999, then edit its digits. See the score and badge change instantly, discover new patterns and try the best single-digit improvement.
The leading slot skips 0 so the digit count stays where you put it — use the length control to change it. 1,000,000 is the only seven-digit number in range; see it here.
No single digit change improves on this number — it is a local maximum.
How to use it
Click any digit slot, then use ↑ and ↓ to step it, ← → to move between slots, or just type a digit. Nothing is sent anywhere — the whole range is scored in your browser from the same index the rest of the site uses.
Why the starting number is 524,287
524,287 is 219 − 1, a Mersenne prime. That makes it prime, a binary repunit and a binary palindrome simultaneously — three traits resting on one arithmetic fact. Change any digit and all three vanish together, which is the shortest possible demonstration of what this tool is for.
Local maxima
"Best single-digit edit" scores every number one edit away and reports the strongest. When it says there is none, you have found a local maximum: a number that no single digit change can improve. They are more common than they sound, and climbing out of one usually means changing two digits at once — which is where the pattern explorer is the better tool.