Play · then understand
Make the impossible feel inevitable.
Number tricks are not really tricks. They are patterns hiding in plain sight. Try a mind reader, land on 1089, and chase 6174—then uncover the mathematics behind each surprise.
✦ Free to play · no account · every secret explained
Number Mind Reader
Choose a number from 1 to 63. For each card, press the button if your number appears on it.
Select the cards that contain your number.
The secret
Each card starts with a power of two: 1, 2, 4, 8, 16, or 32. Adding the powers for the cards you selected reconstructs your number's binary representation.
A place-value surprise
1089 Magic
Use a three-digit number whose first and last digits differ. Reverse, subtract the smaller from the larger, reverse again, and add.
The result is always 1089 for valid inputs because the place-value subtraction leaves a predictable digit pattern.
Kaprekar’s constant
6174 Mystery
Enter four digits with at least two different digits. NumberTrove sorts them, subtracts the smaller order from the larger, and repeats.
Kaprekar's constant is a curious fixed point of this digit routine for most valid four-digit starts.