Sawtooth 181
Sawtooth 181  
View static image  
Pattern type  Sawtooth  

Number of cells  181  
Bounding box  78×87  
Expansion factor  121  
Discovered by  Chris Cain  
Year of discovery  2015  

Sawtooth 181 is a diagonal sawtooth discovered on April 28th, 2015 by Chris Cain,^{[1]} based on a suggestion by Dongook Lee and initial twoglider shotgun constructed by Brett Berger. It was the smallest known sawtooth in terms of its minimum repeating population of 181, until being superseded by Sawtooth 177 (which differs only in the phases of the constituent guns).
The sawtooth functions by letting two glider streams of period 120 retract a block, created by collision with a spark from a 58P5H1V1, one cell at a time. The retracted block is deleted via interaction with a pentadecathlon, and the streams are allowed to return to the nowfartheraway 58P5H1V1 to create another block.
Population
The population is equal to 181 at generations 0, 6960, 849120, 102750480, ..., 58 * (121^{n}  1), ..., giving an expansion factor of 121.
References
 ↑ Chris Cain (April 28, 2015). "Re: Smaller sawtooth". ConwayLife.com forums. Retrieved on July 3, 2016.