This is a neat trick to try while waiting for food to arrive at the restaurant.
Pick any digit and write it down three times. Perhaps you’ve chosen 333 or 888.
Add the 3 digits together:
3 + 3 +3=9 or
8 +8+8= 24
Now divide your original three digit number (333 or 888) by the sum of the digit (9 or 24).
You will get an answer: 37
Why is that so? It is a universal truth. 37 is a prime number.
From “Things to make and do in the Fourth Dimension” by Matt Parker