Presto
Pick a three-digit number (example: 412).
Double it to create a six-digit number (412412).
Divide the result successively by 7, by 11, and by 13. There will be no remainders.
The result is the original number.
An idler's miscellany of compendious amusements
Pick a three-digit number (example: 412).
Double it to create a six-digit number (412412).
Divide the result successively by 7, by 11, and by 13. There will be no remainders.
The result is the original number.
