3、Given in the sequence $\left\{a_{n}\right\}, a_{1}=1, a_{2}=3$, and for any $n \in N_{+}$, $a_{n+2} \leq a_{n}+3 \times 2^{n}$, $a_{n+1} \geq 2 a_{n}+1$ hold. Then the general term formula of the sequence $\left\{a_{n}\right\}$ is $\qquad$