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Every number has a test for divisibility. The issue is that the tests get more complicated as the divisor increases. For primes up to 50, see either of the attached links.
You could combine the tests for divisibility by 3 and 4. To test for divisibility by three, add all the digits together and see if they're divisible by three. If necessary, you can keep repeating the addition until you come up with a single-digit number. To test for divisibility by four, take the last two digits. If that two-digit number is divisible by four, then the whole number is. This is because any multiple of 100 is divisible by 4, so only the last two digits matter. Combined, these two tests will allow you to quickly check for divisibility by 12.
2,3,9,6
10,5,3
2.50