521

Number
$521$ (five hundred and twenty-one) is:


 * The $98$th prime number


 * The $13$th Lucas number after $(2)$, $1$, $3$, $4$, $7$, $11$, $18$, $29$, $47$, $76$, $123$, $199$, $322$:
 * $521 = 199 + 322$


 * The $7$th Lucas prime after $2$, $3$, $7$, $11$, $29$, $199$.


 * The $1$st of the $25$th pair of twin primes:
 * $523 - 521 = 2$