Base 4 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
| 221: | \[{4^{221}-1\over3}\] | 443 × 1327 × 2731 × 8191 × 43691 × 131071 × 4714692062809<13> × 4507513575406446515845401458366741487526913<43> × 2365454398418399772605086209214363458552839866247069233<55> |