A383369 Population of elementary triangular automaton rule 90 at generation n, starting from a lone 1 cell at generation 0.

1, 4, 6, 12, 6, 24, 24, 48, 6, 24, 36, 72, 24, 96, 96, 192, 6, 24, 36, 72, 36, 144, 144, 288, 24, 96, 144, 288, 96, 384, 384, 768, 6, 24, 36, 72, 36, 144, 144, 288, 36, 144, 216, 432, 144, 576, 576, 1152, 24, 96, 144, 288, 144, 576, 576, 1152, 96, 384, 576, 1152, 384, 1536, 1536, 3072, 6

Offset: 0

Author

Paul Cousin, Apr 24 2025

Keywords

• nonn

Comments

An Elementary Triangular Automaton (ETA) is a cellular automaton in the triangular grid where cells hold binary states and rules are local to the first neighborhood. There are 256 possible ETA rules.

Rule 90 (1011010 in binary):

-----------------------------------------------

|state of the cell |1|1|1|1|0|0|0|0|

|sum of the neighbors' states |3|2|1|0|3|2|1|0|

|cell's next state |0|1|0|1|1|0|1|0|

-----------------------------------------------

This is one of the 4 ETA rules (85, 90, 165 and 170) that replicates the pattern given as initial condition.

Examples

			Written as an irregular triangle with row lengths A000079, starting from n=1, the sequence begins:
  4;
  6, 12;
  6, 24, 24, 48;
  6, 24, 36, 72, 24, 96, 96, 192;
  6, 24, 36, 72, 36, 144, 144, 288, 24, 96, 144, 288, 96, 384, 384, 768;
...
It appears that the right border gives A110594.
		

Links

• Paul Cousin, Table of n, a(n) for n = 0..16384
• Paul Cousin, Illustration for n = 0..128
• Paul Cousin, Triangular Automata
• Paul Cousin, Rule 90
• Paul Cousin, Triangular Automata Integer Sequences
• Paul Cousin, Triangular Automata: The 256 Elementary Cellular Automata of the Two-Dimensional Plane, Complex Systems, 33(3), 2024, pp. 253-276.

Crossrefs

Pattern replicating ETA rules: A275667 (rule 170).

A247640 is a bisection.

A246035 is the analog on the square cells.