Base 2 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
| 391: | \[2^{391}-1\] | 47 × 37537 × 131071 × 178481 × 25806248225716242845491832244899635927231330561<47> × 4735299062751047834629348947476766642710028552319600543<55> |