Divisor 20781

To determine if any number is divisible by 20781, you must apply 2 tests successively. If all of them 'pass' - that is, if your number is divisible by 9 and 2309 - then it is divisible by 20781.

The following tests must pass:

• Test if a number is divisible by 9
• The "Tom Gidden Test" for Divisibility by 2309

Easy!