Base 21 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
99: | \[{21^{99}-1\over20}\] | 67 × 463 × 85775383 × 17513875027111<14> × 782006960636353<15> × 146354764854514987<18> × 3955202198062795629622003<25> × 188145268678304791443009491673532813732054627291<48> |