Base 21 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
| 67: | \[{21^{67}-1\over20}\] | 269 × 324363426169571<15> × 312929837239650768379490219650039<33> × 71028332352256443443129296219339913167<38> |