Base 21 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
| 71: | \[{21^{71}-1\over20}\] | 493509073 × 6912925952086714539251625713<28> × 110556144297525239244017467747224789359885811468762753179<57> |