# Repunit Factors

A repunit is an integer that consists of only copies of the digit $$1$$. Let $$R_n$$ be a repunit with $$n$$ digits. Let a ministring be a sequence of digits composed of a nonnegative integer amount of the ' $$0$$' digit followed by a positive integer number of the ' $$1$$' digit. Find the number of divisors of $$R_{20}$$ that consist entirely of copies of a single ministring.

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