991

Number
$991$ (nine hundred and ninety-one) is:


 * The $167$th prime number


 * The $9$th of the sequence of $n$ such that $p_n \# - 1$, where $p_n \#$ denotes primorial of $n$, is prime:
 * $3$, $5$, $11$, $13$, $41$, $89$, $317$, $337$, $991$