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CAT 2020 Slot 1 · Quant · Remainders and Divisibility · medium

What is the remainder when 3²⁵⁶ is divided by 17?

Numerical answer

What is the remainder when 3²⁵⁶ is divided by 17?
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Answer: 1

17 is prime, so by Fermat's little theorem 3¹⁶ ≡ 1 (mod 17).

256 = 16 × 16, so 3²⁵⁶ = (3¹⁶)¹⁶ ≡ 1¹⁶ = 1 (mod 17).

Remainder = 1.

Tip: When the exponent is an exact multiple of (p − 1), the remainder is 1 immediately — check for this special case before doing any further reduction.
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