Just like Fibonacci

Let $\{a_r\}$ be a sequence of positive integers such that $a_r = a_{r-1} + a_{r-2}$ for $r\ge3$ and $a_2=4$ . It is given that $a_n+2a_{n-1}+a_{n-2}=123$ (such that $a_{n+2}$ is the last term of the sequence). Find the value of $\frac{1}{na_1}\sum _{ r=1 }^{ r=n }{ a_r } +\frac{4}{a_1}$