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The $2021$ number is written in such a way that the number with any two consecutive numbers is divisible by either $17$ or $23.$ If the last digit is $7,$ what is the first digit?
Number Theory BdMO
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The $2021$ number is written in such a way that the number with any two consecutive numbers is divisible by either $17$ or $23.$ If the last digit is $7,$ what is the first digit?