Base 4 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
| 263: | \[{4^{263}-1\over3}\] | 1579 × 23671 × 92051 × 13572264529177<14> × 29261114397558193<17> × 120226360536848498024035943<27> × 383725126655170964501315730676446647<36> × 1161625406204540347970098063703363946902736086742697099<55> |