Base 21 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
50: | \[{21^{50}-1\over20}\] | 2 × 52 × 11 × 101 × 40841 × 185641 × 2031851 × 11093851 × 248303068144516751<18> × 27385718497004633851<20> |