Base 4 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
| 121: | \[{4^{121}-1\over3}\] | 23 × 89 × 683 × 727 × 117371 × 11054184582797800455736061107<29> × 1786393878363164227858270210279<31> |