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Number theory Difficulty 2.6 Junior Find the answer

The integer 2023 is equal to 7imes1727 imes 17^{2}. Which of the following is the smallest positive perfect square that is a multiple of 2023?

A number or a short expression. Spacing and $ signs are ignored.

Solution

Since 2023=7imes1722023=7 imes 17^{2}, then any perfect square that is a multiple of 2023 must have prime factors of both 7 and 17. Furthermore, the exponents of the prime factors of a perfect square must be all even. Therefore, any perfect square that is a multiple of 2023 must be divisible by 727^{2} and by 17217^{2}, and so it is at least 72imes1727^{2} imes 17^{2} which equals 7imes20237 imes 2023. Therefore, the smallest perfect square that is a multiple of 2023 is 7imes20237 imes 2023. We can check that 202322023^{2} is larger than 7imes20237 imes 2023 and that none of 4imes20234 imes 2023 and 17imes202317 imes 2023 and 7imes17imes20237 imes 17 imes 2023 is a perfect square.

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