Gọi [tex]d=(\frac{n(n+1)}{2},2n+1)[/tex] [tex](d\in \mathbb{N}^{*})[/tex]
[tex]\Rightarrow \left\{\begin{matrix} 2n^{2}+2n\vdots d\\ 2n+1\vdots d \end{matrix}\right.[/tex]
[tex]\Leftrightarrow \left\{\begin{matrix} n(2n+1)+n\vdots d\\ 2n+1\vdots d \end{matrix}\right.[/tex]
[tex]\Leftrightarrow \left\{\begin{matrix} n\vdots d\\ 2n+1\vdots d \end{matrix}\right.[/tex]
[tex]\Rightarrow 1\vdots d[/tex]
[tex]\Rightarrow d=1[/tex]