523

Number
$523$ (five hundred and twenty-three) is:


 * The $99$th prime number


 * The $1$st element of the $1$st sequence of $3$ consecutive positive integers whose Euler $\phi$ values are strictly decreasing:
 * $\map \phi {523} = 522$, $\map \phi {524} = 260$, $\map \phi {525} = 240$


 * The $2$nd of the $25$th pair of twin primes:
 * $523 - 521 = 2$

Also see

 * First Sequence of Three Consecutive Strictly Decreasing Euler Phi Values