n!!!! + 1
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
256: | \[256!!!!+1\] | 65123 × 176227 × 22702567 × 1410285496315790528506513180199<31> × 311251709299821141697754231708087<33> × 377533717667011188341026671402738336811798605311<48> |