jmc

To get from the $1^{\text{st}}$ term of an arithmetic sequence to the $100^{\text{th}}$ term, we must add the common difference $99$ times. The first term is $1$ and the common difference is $5-1=9-5=13-9=\cdots =4$, so the $100^{\text{th}}$ term is $$1+4(99)=397\to \boxed{397}$$