1,111,111,111,111,111,111

Number
$1 \, 111 \, 111 \, 111 \, 111 \, 111 \, 111$ is:


 * A prime number


 * The $2$nd repunit prime


 * The $13$th unique period prime after $3$, $11$, $37$, $101$, $9091$, $9901$, $333 \, 667$, $909 \, 091$, $99 \, 990 \, 001$, $999 \, 999 \, 000 \, 001$, $9 \, 999 \, 999 \, 900 \, 000 \, 001$, $909 \, 090 \, 909 \, 090 \, 909 \, 091$: its period is $19$:
 * $\dfrac 1 {1 \, 111 \, 111 \, 111 \, 111 \, 111 \, 111} = 0 \cdotp \dot 00000 \, 00000 \, 00000 \, 000 \dot 9$


 * The $19$th repunit


 * The $23$rd permutable prime after $2$, $3$, $5$, $7$, $11$, $13$, $17$, $31$, $37$, $71$, $73$, $79$, $97$, $113$, $131$, $199$, $311$, $337$, $373$, $733$, $919$, $991$

Also see

 * Repunit 19 is Unique Period Prime with Period 19