Base 4 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
251: | \[{4^{251}-1\over3}\] | 503 × 54217 × 238451 × 178230287214063289511<21> × 61676882198695257501367<23> × 12070396178249893039969681<26> × 5058345723951854688505665428846313806490903121677364358901199128608233<70> |