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UKMT Intermediate Mathematical Challenge, 2026

Number theory Difficulty 2.0 Junior Find the answer United Kingdom

How many of the following expressions are divisible by 24? $5^2-1$ $\quad$ $7^2-1$ $\quad$ $9^2-1$ $\quad$ $11^2-1$ $\quad$ $13^2-1$

(A) $1$ (B) $2$ (C) $3$ (D) $4$ (E) $5$

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