Base 2 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
| 238: | \[2^{238}-1\] | 3 × 43 × 127 × 239 × 20231 × 43691 × 131071 × 823679683 × 62983048367<11> × 131105292137<12> × 143162553165560959297<21> |