Base 4 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
| 281: | \[{4^{281}-1\over3}\] | 563 × 80929 × 5203536083<10> × 442079688503172860176607217752424068059658864615965341384647107224486419<72> × 48009215293052652841860443273079338843737271906291675944391068955229998769420319<80> |