Base 21 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
76: | \[{21^{76}-1\over20}\] | 22 × 11 × 13 × 17 × 229 × 457 × 609673 × 12061389013<11> × 54921106624003<14> × 987749814642143197<18> × 3794540985952206860593938878074866571399837<43> |