A semi-cenark is either of two semi-Snark variants discovered by Tanner Jacobi in November 2017. The name is due to the initial converter, which produces a century output for every two input gliders. The minimum safe repeat time is 43 ticks for the smaller initial catalyst shown in CC semi-cenark and CP semi-cenark, or 42 ticks with the slightly larger catalyst variant shown below.
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There is also the possibility of overclocking at period 36, 38, or 39. The reset glider can be followed immediately by a new trigger glider, as shown above, so the minimum repeat time for an intermittent stream of gliders is only 36 + 14 = 50 ticks.
The semi-cenarks were part of a series of new stable pulse dividers (the others being the tremi-Snark and the quadri-Snark) which collectively ranked third place in the Pattern of the Year 2017 competition on the ConwayLife.com forums, behind Tanner's p46 and the 2-engine Cordership.
- Tanner Jacobi (November 3, 2017). Re: Execution of Old Guns by Variable-Speed Firing Squad (discussion thread) at the ConwayLife.com forums
- Dave Greene (February 19, 2018). Re: Pattern of the Year 2017 -- votes (discussion thread) at the ConwayLife.com forums