Base 21 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
89: | \[{21^{89}-1\over20}\] | 138348511207<12> × 1719937817227174896868741057213630597485253956382680484361683645714455944660556942937263903929864448451087<106> |