Divisor 20991

To determine if any number is divisible by 20991, you must apply 2 tests successively. If all of them 'pass' - that is, if your number is divisible by 3 and 6997 - then it is divisible by 20991.

The following tests must pass:

• Test if a number is divisible by 3
• The "Benjamin Mishler Test" for Divisibility by 6997

Easy!