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lfdahl

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Prove the existence of a positive integer divisible by $2019$ the sum of whose decimal digits is $2019$.

Source: Nordic Math. Contest

Source: Nordic Math. Contest

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lfdahl

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Source: Nordic Math. Contest

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Opalg

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[sp]$2019$ has digital sum $12$. Twice $2019$ is $4038$, which has digital sum $15$. Also, $$2019 = 15 + 2004 = 15 + 12\cdot167.$$ So the number $$4038\;\overbrace{2019\;2019\;\ldots\;2019}^{167\text{ blocks}},$$ whose decimal expansion consists of $4038$ followed by $167$ blocks of $2019$, has decimal sum $2019$. It is clearly a multiple of $2019$, the quotient being $$2\;\overbrace{0001\;0001\;\ldots\;0001}^{167\text{ blocks}}.$$

Source: Nordic Math. Contest

[/sp]

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lfdahl

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Thankyou, Opalg, for your participation and - as always - for a clever answer! (Yes)

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