181

Number
$181$ (one hundred and eighty-one) is:


 * The $42$nd prime number


 * The $2$nd of the $13$th pair of twin primes, with $179$


 * The $9$th palindromic prime:
 * $2$, $3$, $5$, $7$, $11$, $101$, $131$, $151$, $181$, $\ldots$


 * The smaller of the $2$nd pair of primes whose prime gap is $10$:
 * $191 - 181 = 10$


 * The $12$th prime number after $53$, $71$, $103$, $107$, $109$, $149$, $151$, $157$, $163$, $167$, $173$ which cannot be expressed as the difference between a power of $2$ and a power of $3$.