Base 4 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
| 181: | \[{4^{181}-1\over3}\] | 1811 × 43441 × 1164193 × 7648337 × 31675363 × 7923871097285295625344647665764672671<37> × 17810163630112624579342811733978085990447907<44> |