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Question

Find the remainder: \( (17^{13} - 21) \div 18 \).

This question was previously asked in
SSC CGL 2024 (Tier-I) Previous Year Paper (17-Sep-2024) (Shift 3)
The correct answer is

14

We need to find the remainder when \( 17^{13} - 21 \) is divided by 18.

Step 1: Apply Fermat’s Theorem:

\( 17 \equiv -1 \pmod{18} \).

Step 2: Compute \( 17^{13} \) mod 18:

\( (-1)^{13} \equiv -1 \pmod{18} \).

Step 3: Compute \( (-1 - 21) \mod 18 \):

\( -22 \mod 18 = 14 \).

Thus, the remainder is 14.

The correct answer is option 1.

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