Base 21 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
73: | \[{21^{73}-1\over20}\] | 30661 × 5424905842809814580790135175148153005273370039115139875248165723989059011789226683837426053<91> |