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UKMT Junior Mathematical Challenge, 2016

Number theory Difficulty 1.0 Junior Find the answer United Kingdom

How many of these four expressions are perfect squares? $1^3+2^3$ , $1^3+2^3+3^3$ , $1^3+2^3+3^3+4^3$ , $1^3+2^3+3^3+4^3+5^3$

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

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