Base 21 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
| 79: | \[{21^{79}-1\over20}\] | 2687 × 10903 × 15208288358346544216626697<26> × 122435283552586211204658864416622901<36> × 261513239159154440967606433092726647<36> |