Base 21 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
| 75: | \[{21^{75}-1\over20}\] | 52 × 151 × 211 × 463 × 1051 × 1801 × 9391 × 18181 × 40841 × 2031851 × 9728219701<10> × 201307465501<12> × 27385718497004633851<20> × 138288178346489520230701<24> |