Problem 303

Multiples with small digits

For a positive integer `n`, define `f`(`n`) as the least positive multiple of `n` that, written in base 10, uses only digits 2.

Thus `f`(2)=2, `f`(3)=12, `f`(7)=21, `f`(42)=210, `f`(89)=1121222.

Also, .

Find .

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