1021

Number
$1021$ (one thousand and twenty-one) is:


 * The $172$nd 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:
 * $2$, $3$, $5$, $7$, $11$, $31$, $379$, $1019$, $1021$


 * The smaller of the $17$th pair of primes whose prime gap is $10$:
 * $1031 - 1021 = 10$


 * The $35$th emirp after $13$, $17$, $31$, $37$, $\ldots$, $733$, $739$, $743$, $751$, $761$, $769$, $907$, $937$, $941$, $953$, $967$, $971$, $983$, $991$, $1009$


 * The larger of the $36$th pair of twin primes:
 * $1021 - 1019 = 2$

Also see