Kayasari Ryuunosuke.you should write \(2n+3\in D\left(5\right)\)

P is a natural number 

<=> 4n + 1 \(⋮\) 2n + 3

<=> 4n + 6 - 6 + 1 \(⋮\) 2n + 3

<=> 2(2n + 3) - 5 \(⋮\) 2n + 3

<=> 5 \(⋮\) 2n + 3

=> 2n + 3 \(\inƯ\left(5\right)=\left\{1;-1;5;-5\right\}\)

We have a table :

Hence , n = {-1 ; -2 ; 1 ; 4}

\(⋮\)