Is the number N divisible by…. 2? 3? 5?
Everyone knows the first trick:
N is divisible by 2 if its last digit is 0, 2, 4, 6, or 8 (that is, last digit is even).
Most people know the next trick:
N is divisible by 3 if the sum of the digits is also divisible by 3.
You can repeat this rule too.
For example: Is the number 93,225 is divisible by 3? Well…
And, 21 is divisible by 3, hence 93,225 is divisible by 3.
N is divisible by 4 if the last two digist form a number divisible by 4.
do an example: Is the number 23894723985729316 divisible by 4? Well the
last two digits is 16 and 16 is divisible by 4, so YES!
N is divisible by 5 if it ends in 0 or 5.
For 6, we just combine the rules for 2 and 3:
N is divisible by 6 if it is divisible by both 2 and 3.
For the rest, we will stick with prime divisors p.
Consider multiples M of p until:
We want the smallest such M.
Consider n and p-n, and usually we just pick the lowest.
to find out if a number is divisible by p, take the last digit of the
number, multiply it by n, and add it to the rest of the number (OR:
multiply it by (p – n) and subtract it from the rest of the number).
If you get an answer divisible by p (note that this includes 0), then
the original number is divisible by p. Repeat the rule if you don’t
know the new number’s divisibility.