Base 4 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
| 257: | \[{4^{257}-1\over3}\] | 37239639534523<14> × 535006138814359<15> × 518144156602508243009<21> × 1155685395246619182673033<25> × 374550598501810936581776630096313181393<39> × 4000659204579114753312310878847043394855313<43> |