Base 21 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
| 74: | \[{21^{74}-1\over20}\] | 2 × 11 × 31081 × 1681762703 × 7995105693353508392600118377453099<34> × 379919184478057330357419845346252603881265273961<48> |