Base 21 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
| 169: | \[{21^{169}-1\over20}\] | 79 × 189437 × 516094151 × 787331117 × 51032784753339594393762302249756328003879131971060424025791<59> × 4594130155343871975058851367976626872561710502528706854567172756009712468440851511490609405787706740526924640052740822297629391041650057319<139> |