Find the 6th\displaystyle {6}^{{{t}{h}}} term of the recursive sequence {a1=18a2=7an=an1+an2\displaystyle {\left\lbrace\begin{array}{c} {a}_{{1}}={18}\\{a}_{{2}}={7}\\{a}_{{n}}={a}_{{{n}-{1}}}+{a}_{{{n}-{2}}}\end{array}\right.}

a6=\displaystyle {a}_{{6}}=