Base 4 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
| 219: | \[{4^{219}-1\over3}\] | 3 × 7 × 439 × 1753 × 3943 × 2298041 × 9361973132609<13> × 9070197542196643<16> × 671165898617413417<18> × 1795918038741070627<19> × 4815314615204347717321<22> × 3278244690156222434135906137<28> |