Guide to finding out if numbers are multiples quickly

0. It is

This also means 0 is a multiple of all numbers.

1. It is

Ex: 57 is a multiple of 1

2. Ignore everything except the last digit.

Ex: 46394628 is a multiple of 2.

3. Add all the digits and if they’re a multiple of 3, so is the number.

Ex: 12, 1+2=3, confirmed

564852, 5+6+4+8+5+2=30, confirmed.

4. Ignore everything except the last two digits.

Ex: 46354816 is a multiple of 4.

5. If the last digit is a multiple of 5.

Ex: 473525 is a multiple of 5.

6. If it’s a multiple of 2 and 3.

Ex: 56442 is even and all digits add up to 21 so it is.

7. Take the last digit, double it, and subtract is from the rest of the number.

Ex: 49, 4-18=-7, confirmed

112, 11-4=7, confirmed

8. Ignore everything except the last 3 digits.

Ex: 45024 is a multiple.

This pattern of adding a digit continues for all powers of 2 and all powers of 5.

9. If all the digits add up to a multiple of 9.

Ex: 81, 8+1=9, confirmed

189, 1+8+9=18, confirmed

I presume this pattern continues for all powers of 3.

10. If the last two digits are a multiple of 10 (or if the last digit is 0).

Ex: 36450

Pattern also continues for powers of 10.

11. Number the digits, add all the odd digits to the sum, subtract all the even digits from the sun, and see if it’s a multiple of 11.

Ex: 121, (+)1-2+1=0, confirmed

121414, (+)1-2+1-4+1-4=-7, confirmed

12. See if it’s a multiple of 4 and 3.

Ex: 144, 1+4+4=9, confirmed

13. Quadruple the last digit and add it to the rest of the number and see if it’s a multiple of 13.

Ex: 169, 16+36=52, confirmed

247, 24+28=52, confirmed

14. See if it’s a multiple of 2 and 7.

Ex: 196, 19-12=7, confirmed

15. See if it’s a multiple of 3 and 5.

Ex: 75, 7+5=12, confirmed

This seeing if it’s a multiple of 2 numbers only works if the numbers aren’t multiples of each other.