Base 2 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
| 208: | \[2^{208}-1\] | 3 × 5 × 17 × 53 × 157 × 257 × 1613 × 2731 × 8191 × 858001 × 308761441 × 78919881726271091143763623681<29> |