991

Number

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

The $9$th prime $p$ such that $p \# - 1$, where $p \#$ denotes primorial (product of all primes up to $p$) of $p$, is prime:

$3$, $5$, $11$, $13$, $41$, $89$, $317$, $337$, $991$

The $14$th minimal prime base $10$ after $2$, $3$, $5$, $7$, $11$, $19$, $41$, $61$, $89$, $409$, $449$, $499$, $881$

The larger of the $15$th pair of primes whose prime gap is $8$:

$991 - 983 = 8$

The $22$nd permutable prime after $2$, $3$, $5$, $7$, $11$, $13$, $17$, $31$, $37$, $71$, $73$, $79$, $97$, $113$, $131$, $199$, $311$, $337$, $373$, $733$, $919$

The $33$rd emirp after $13$, $17$, $31$, $37$, $\ldots$, $733$, $739$, $743$, $751$, $761$, $769$, $907$, $937$, $941$, $953$, $967$, $971$, $983$

The $45$th near-repdigit prime after $101$, $113$, $131$, $151$, $\ldots$, $727$, $733$, $757$, $773$, $787$, $797$, $811$, $877$, $881$, $883$, $887$, $911$, $919$, $929$, $977$