Base 4 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
| 217: | \[{4^{217}-1\over3}\] | 43 × 127 × 5209 × 62497 × 16233337 × 715827883 × 2147483647 × 6268703933840364033151<22> × 378428804431424484082633<24> × 140508608590164280225934233098866842745808905947<48> |