Divisor 21989

To determine if any number is divisible by 21989, you must apply 2 tests successively. If all of them 'pass' - that is, if your number is divisible by 11 and 1999 - then it is divisible by 21989.

The following tests must pass:

• Test if a number is divisible by 11
• The "Stuart Sewell Test" for Divisibility by 1999

Easy!