在数列<img class="kfformula" src="20190809/1565316783973080.png" data-latex="\left \{ {{a}_{n}} \right \} "/>中,前<img class="kfformula" src="20190809/1565316783992384.png" data-latex="n"/>项和公式是<img class="kfformula" src="20190809/1565316783683277.png" data-latex="{s}_{n}=4{n}^{2}-n"/>,那么<img class="kfformula" src="20190809/1565316783325652.png" data-latex="{a}_{2}"/>为( )