Base 21 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
66: | \[{21^{66}-1\over20}\] | 2 × 112 × 23 × 67 × 421 × 463 × 3499 × 6073 × 28513 × 33199 × 10362529 × 17513875027111<14> × 87989435079877<14> × 3955202198062795629622003<25> |