Base 21 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
49: | \[{21^{49}-1\over20}\] | 43 × 631 × 3319 × 7057 × 1606344741163<13> × 1767442850839<13> × 1703751007820049542146461103<28> |