1.$\left\{\begin{matrix}u_1=1
& \\ u_{n+1}=u_n+\sqrt{n+1}
&
\end{matrix}\right.$
2.$\left\{\begin{matrix}u_1=2
& \\ u_{n+1}=\dfrac{u_{n}^{4}+12u_{n}^{2}+4}{4u_{n}^{2}+8u_n}
&
\end{matrix}\right.$
3. $\left\{\begin{matrix}u_1=2
& \\ u_{n+1}=\sqrt{2}+\sqrt{u_{n}^{2}+1}
&
\end{matrix}\right.$
