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UKMT Intermediate Mathematical Challenge, 2016

Number theory Difficulty 1.0 Junior Find the answer United Kingdom

How many of these five expressions give answers which are not prime numbers? $1^2 + 2^2$ , $2^2 + 3^2$ , $3^2 + 4^2$ , $4^2 + 5^2$ , $5^2 + 6^2$

(A) $0$ (B) $1$ (C) $2$ (D) $3$ (E) $4$

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