3 links
Digital Divisibility Tests
primepuzzles.net
From Carlos Rivera's Prime Puzzles and Problems collection. Carlos asks for the general divisibility rules for any prime number.
Explaining the Divisibility Rules
mathforum.org
Proof of the elementary division rules, plus some lesser-known rules for larger divisors and other bases.
The Anti-Divisor
users.globalnet.co.uk
Introduction to unbiased non-divisor and using it in mathematical proofs.