Cellular automaton [Nand] formulas

For 1 step, the elementary cellular automaton rules are exactly the 256n = 3 Boolean functions. For 2 steps, they represent a small subset of the2³²n = 5 functions. They require an average of about 11.6Nand operations, and a maximum of 27 (achieved by rules 107 and 121).

For rule 254 the result aftert steps (which is always asymmetric, even though the rule is symmetric) is

Nest[{{#, #〚2〛 + 1}, #〚2〛 + 1} &, {{1, 1}, {2, 2}}, t - 2]

If explicit copy operations were allowed, then the number ofNand operations aftert steps could not increase faster thant² for any rule. But without copy (fanout) operations no corresponding result is immediately clear.