Base 4 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
| 131: | \[{4^{131}-1\over3}\] | 263 × 1049 × 4744297 × 182331128681207781784391813611<30> × 10350794431055162386718619237468234569<38> |