317/Mistake

Source Work

 * The Dictionary
 * $11,111,111, \ldots 111,111$
 * $11,111,111, \ldots 111,111$

Mistake

 * The $3$rd known prime repunit.

Correction
The $4$th known, in fact, after $R_2$, $R_{19}$ and $R_{23}$.

This mistake does not appear in of $1986$, where it states:


 * The $4$th and largest known prime repunit.

Some considerably larger ones have been discovered since.