How to check if a number divides a very large number using modulo

55 Views Asked by At

How would I determine if 13 divides 1212 -1

I know the question's asking if 1212 is congruent to 1 (mod 13), but how would I go about solving this without a calculator?

2

There are 2 best solutions below

0
On

Hint: $$12\equiv -1\mod 13$$ so $$12^{12}\equiv (-1)^{12}\mod 13$$

0
On

Hint: (without the use of congruences)

$$12^{12}-1=(13-1)^{12}-1$$

When expanding the parentheses, how many terms are not divisible by $13$?