- 15 is an odd composite number.
- 15 is the 5th triangular number.
- 15 is equal to 5!!, the double factorial of 5.
- In Czech language, 15 is called "mandel".
- 15 is the product of the first two Fermat primes.
- The integral part of ee is equal to 15.
In Greek-based naming systems, 15 is associated with prefix "pentadeka-", and with prefix "quindeci-" in Latin systems.
As a banknote denomination
The third Burmese kyat had banknotes with this number in the denomination.
- Britannica, Fifteen Puzzle