Divisor 20721

To determine if any number is divisible by 20721, you must apply 2 tests successively. If all of them 'pass' - that is, if your number is divisible by 3 and 6907 - then it is divisible by 20721.

The following tests must pass:

• Test if a number is divisible by 3
• The "Tom G Test" for Divisibility by 6907

Easy!