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Very nice and very famous too! 1991|1999999....91

Source: Problem 4, Brazilian MO, 1991

March 19, 2006
Eulermodular arithmeticpigeonhole principlenumber theory proposednumber theory

Problem Statement

Show that there exists n>2n>2 such that 1991∣1999…911991 | 1999 \ldots 91 (with nn 9's).
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