Base 21 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
| 128: | \[{21^{128}-1\over20}\] | 27 × 11 × 13 × 17 × 257 × 641 × 1217 × 1409 × 2689 × 31873 × 62897 × 97241 × 300673 × 527489 × 6857635489<10> × 70660081537<11> × 1023263388750334684164671319051311082339521<43> × 242055625097457531000185232276713458675446736812859343682689<60> |