Ta có :
\(26n⋮2n-1\)
Mà \(2n-1⋮2n-1\)
\(\Leftrightarrow\hept{\begin{cases}26n⋮2n-1\\26n-13⋮2n-1\end{cases}}\)
\(\Leftrightarrow13⋮2n-1\)
Vì \(n\in N\Leftrightarrow2n-1\in N;2n-1\inƯ\left(13\right)\)
\(\Leftrightarrow\orbr{\begin{cases}2n-1=1\\2n-1=13\end{cases}}\) \(\Leftrightarrow\hept{\begin{cases}n=1\\n=7\end{cases}}\)
Vậy ..