Coral

The rule

In Softology's notation 5-8/6-7,9,12/4/M: a live cell survives with 5 to 8 live neighbours, a dead cell is born with 6, 7, 9 or 12, and there are 4 states, so a cell that fails to survive spends two generations dying.

What it does

From its start, a random block half the box wide and half full, it grows outward like coral. It never settled in our test: in 20 seeded runs in a 30×30×30 box, every one was still changing after 300 generations, with 26% to 28% of the box alive.

Run Coral from its start →

How the rule works

• Each cell has 26 neighbours: every cell that shares a face, an edge or a corner with it (the Moore neighbourhood).
• An empty cell comes alive when 6, 7, 9 or 12 of its neighbours are alive.
• A live cell stays alive when 5 to 8 of its neighbours are alive; otherwise it starts dying: for 2 generations it fades, is not counted as a neighbour and blocks births, then the cell is empty again.
• With 4 states in all (alive, 2 dying, dead), this is a Generations rule.

Picking it in the app restarts the world from a random block in the middle of the box, 50% full and half as wide as the box. Its seed is fixed, so it is the same world every time, one still alive 40 generations later in the default 15×15×15 box; N tries another seed.

Notation

B lists the neighbour counts at which an empty cell is born, S those at which a live cell survives, and C the number of states. How to read a rule

More of Softology's rules

• 445 B4/S4/C5
• Amoeba B5-7,12-13,15/S9-26/C5
• Architecture B3/S4-6
• Builder 1 B4,6,8-9/S2,6,9/C10
• Builder 2 B1/S5-7
• Clouds 1 B13-14,17-19/S13-26
• Clouds 2 B13-14/S12-26
• Crystal Growth 1 B1,3/S0-6
• Crystal Growth 2 B1,3/S1-2/C5
• Pyroclastic B6-8/S4-7/C10
• Spiky Growth B13,17,20-26/S0-3,7-9,11-13,18,21-22,24,26/C4
• 3D Brain B4/S

All 30 rules · From 2D to 3D: why Conway's rule needs changing in 3D