Divisor 21591

To determine if any number is divisible by 21591, you must apply 2 tests successively. If all of them 'pass' - that is, if your number is divisible by 9 and 2399 - then it is divisible by 21591.

The following tests must pass:

• Test if a number is divisible by 9
• The "Piotr Jakuc Test" for Divisibility by 2399

Easy!