Divisor 27991

To determine if any number is divisible by 27991, you must apply 2 tests successively. If all of them 'pass' - that is, if your number is divisible by 23 and 1217 - then it is divisible by 27991.

The following tests must pass:

• Test if a number is divisible by 23
• The "Capel Hanbury-Tenison Test" for Divisibility by 1217

Easy!