Base 4 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
| 223: | \[{4^{223}-1\over3}\] | 18287 × 196687 × 1466449 × 2916841 × 219256122131<12> × 1469495262398780123809<22> × 596242599987116128415063<24> × 20493495920905043950407650450918171260318303154708405513<56> |