Base 21 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
78: | \[{21^{78}-1\over20}\] | 2 × 11 × 79 × 421 × 463 × 547 × 1171 × 11701 × 189437 × 629773 × 516094151 × 7021471715414521<16> × 7691526674487958994017<22> × 80459337199345300130638393<26> |