Base 21 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
| 137: | \[{21^{137}-1\over20}\] | 1434935907463<13> × 26713431631673<14> × 45072031559057<14> × 72752932313208962053<20> × 2507048871610995663351125327991556777<37> × 2210704839453987084654529873799609279235272917800596662452622653082037998178772558979<85> |