991

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


 * The $167$th prime number


 * The $9$th prime $p$ such that $p \# - 1$, where $p \#$ denotes primorial (product of all primes up to $p$) of $p$, is prime:
 * $3$, $5$, $11$, $13$, $41$, $89$, $317$, $337$, $991$