Base 21 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
| 163: | \[{21^{163}-1\over20}\] | 13693 × 14599604213<11> × 561788105646941<15> × 71382227518918280601812453<26> × 233873265768022293940710651427<30> × 375293848786689453728783544296310281471843370384860719701298799<63> × 23624394860436672961074440125549492456615261234980975872188679386843<68> |