Base 21 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
64: | \[{21^{64}-1\over20}\] | 26 × 11 × 13 × 17 × 1217 × 2689 × 31873 × 62897 × 97241 × 300673 × 6857635489<10> × 1023263388750334684164671319051311082339521<43> |