Problem
NT-B1-M10-P005 Repunit of Length \(4\)
#5
★☆☆☆☆ Level 1 of 5
Represent \(1111\) in the form \(\frac{10^n-1}{9}\).
It is a number of four ones.
Since \(1111=1+10+10^2+10^3\), we have \(1111=\frac{10^4-1}{9}\).
Introduces the notation \(R_n\).