1. In the arithmetic sequence $\left\{a_{n}\right\}$, the common difference $d \neq 0$, and $a_{2021}=a_{20}+a_{21}$, then the value of $\frac{a_{1}}{d}$ is
$$
a_{1}+2020 d=2 a_{1}+39 d \Rightarrow a_{1}=1981 d \Rightarrow \frac{a_{1}}{d}=1981 .
$$