Divisor 17991

To determine if any number is divisible by 17991, you must apply 2 tests successively. If all of them 'pass' - that is, if your number is divisible by 9 and 1999 - then it is divisible by 17991.

The following tests must pass:

• Test if a number is divisible by 9
• The "Stuart Sewell Test" for Divisibility by 1999

Easy!