JEE Main 2022 · 25 Jul · Shift 1, Mathematics question 25

Let $a_1=b_1=1$, $a_n=a_{n-1}+2$ and $b_n=a_n+b_{n-1}$ for every natural number $n\ge2$. Then $\displaystyle\sum_{n=1}^{15}a_n\cdot b_n$ is equal to ______.