Question: what are all the divisibility rules?
Answer: Any integer (not a fraction) is divisible by 1.
The last digit is even (0,2,4,6,8) ... 
The sum of the digits is divisible by 3. ... 
The last 2 digits are divisible by 4. ... 
The last digit is 0 or 5. ... 
Is even and is divisible by 3 (it passes both the 2 rule and 3 rule above)