MathDB
CNCM Online R3 P5

Source:

November 7, 2020
CNCM

Problem Statement

How many positive integers NN less than 10100010^{1000} are such that NN has xx digits when written in base ten and 1N\frac{1}{N} has xx digits after the decimal point when written in base ten? For example, 20 has two digits and 120\frac{1}{20}= 0.05 has two digits after the decimal point, so 2020 is a valid N.
Proposed by Hari Desikan (HariDesikan)
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