Base 4 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
| 173: | \[{4^{173}-1\over3}\] | 347 × 4153 × 730753 × 1505447 × 35374479827<11> × 47635010587<11> × 70084436712553223<17> × 155285743288572277679887<24> × 1643464247728189221623609<25> |