how will you calculate

^{5^{3^{5^{7^{9}}}}}

find the remainder when divided by 21

(without calculatin)

2 Answers

5³â‰¡-1 (mod 21)
5³ⁿâ‰¡(-1)ⁿ (mod 21)

If n is odd then the answer is -1 (or 20) if it is even then answer is 1

Now can you complete it?

I dont know why the question setter gives without calculation.. (I for one would have died.. but calculated :D)

hehe, it might be of some country wherein caculators or computer find a bigger use than brains do :P

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