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x = 28, y = 21, rule = b3/s23 4b2o4bo4b2o11b$3bo2bobo3bobo2bo10b$3b3o9b3o10b$b2o3b2o5b2o13b$obo2bo2b 5o2bo4b2o6b$obobobo7b2o3bo2bo5b$bobobo13bobo2bo2bo$3bo14b2obob5o$2bo2b o11bo3bo6b$2bo9bo4bo4bob2o2b$2bo3bo3b2ob2o2bo3b2o3bob$2bo9bo4bo4bobobo b$2bo2bo11bo3bo3bo2b$3bo14b2obob2o3b$bobobo13bobobo4b$obobobo7b2o3bobo 2bo3b$obo2bo2b5o2bo4bo2b2o3b$b2o3b2o5b2o13b$3b3o9b3o10b$3bo2bobo3bobo 2bo10b$4b2o4bo4b2o! #C [[ THUMBSIZE 2 THEME 6 GRID GRIDMAJOR 0 SUPPRESS THUMBLAUNCH ]] #C [[ AUTOSTART ]] #C [[ GPS 4 LOOP 20 THUMBSIZE 2 ZOOM 10 ]]
Pattern type Oscillator
Number of cells 145
Bounding box 28×21
Period 20
Mod 20
Heat 72.8
Volatility 0.60
Strict volatility 0.18
Discovered by Noam Elkies
Year of discovery 1995

145P20 is an unnamed period-20 oscillator. It was the first non-trivial period 20 oscillator to be found,[note 1] and was discovered by Noam Elkies on March 22, 1995.[1]

It works by using sparks from three period 4 middleweight emulators and the period 5 middleweight volcano to hassle a traffic light predecessor. The middleweight emulator on the left can be replaced with a middleweight volcano.


  1. A period-20 oscillator, heavyweight emulator on octagon II, can be constructed from two sparkers (heavyweight emulator and octagon II) both of which were known by 1980. However, this type of oscillator is generally considered "boring", and thus not counted despite technically being non-trivial.


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