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CAT 2017 Slot 2 · Quant · Remainders and Divisibility · medium

What is the remainder when 13¹⁵⁰ is divided by 7?

Numerical answer

What is the remainder when 13¹⁵⁰ is divided by 7?
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Answer: 1

13 ≡ 6 ≡ −1 (mod 7).

So 13¹⁵⁰ ≡ (−1)¹⁵⁰ = 1 (mod 7), since 150 is even.

Remainder = 1.

Tip: whenever the base is ≡ −1 (mod n), the parity of the exponent alone decides the remainder — no need for Fermat's theorem here.
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