Base 21 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
68: | \[{21^{68}-1\over20}\] | 22 × 11 × 13 × 172 × 11969 × 300293033 × 114089969144083169<18> × 1502097124754084594737<22> × 399981195234791390040813065378761<33> |