Each cell takes one of 3 states {0,1,2}. The next state depends only on the sum of the cell and its two neighbors (7 possible sums: 0–6), giving 3^7 = 2187 possible rules. Rule 357 is Wolfram's "most interesting."
Rule 357 | Step 0
Outer totalistic 3-color CA: the sum s = left+center+right ∈ {0,1,2,3,4,5,6} encodes the neighborhood. The rule maps each sum to a new state in {0,1,2}. Rule 357 in base 3 (= 111100 in base 3) produces complex nested patterns. Rule space: 3^7=2187 rules. Wolfram (2002): rule 357 was identified as exhibiting complex, class-IV behavior. Connection: 3-color CAs have been shown capable of universal computation.