Divisor 13979

To determine if any number is divisible by 13979, you must apply 2 tests successively. If all of them 'pass' - that is, if your number is divisible by 7 and 1997 - then it is divisible by 13979.

The following tests must pass:

• Test if a number is divisible by 7
• The "Robert Wilson Test" for Divisibility by 1997

Easy!