Base 4 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
| 208: | \[{4^{208}-1\over3}\] | 5 × 17 × 53 × 157 × 257 × 1613 × 2731 × 8191 × 65537 × 858001 × 928513 × 308761441 × 18558466369<11> × 23877647873<11> × 21316654212673<14> × 715668470267111297<18> × 78919881726271091143763623681<29> |