Twenty-five integers $a_1,a_2,a_3,\dots ,a_{25}$ are arranged in order on a number line. The integers are equally spaced and have the property that $1\le a_1\le 12$, $34\le a_5\le 38$, and $156\le a_{25}\le 160$. What is the sum of digits of $a_{20}$?