Divisor 21969

To determine if any number is divisible by 21969, you must apply 2 tests successively. If all of them 'pass' - that is, if your number is divisible by 9 and 2441 - then it is divisible by 21969.

The following tests must pass:

• Test if a number is divisible by 9
• The "William Gross Test" for Divisibility by 2441

Easy!