Base 28 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
| 81: | \[{28^{81}-1\over27}\] | 34 × 192 × 271 × 541 × 444979 × 68948693997660959163751<23> × 467102764647624870534174882972667122829050205740085854715337092963516619074219<78> |