Caterer on 44P7.2 is a period-21 oscillator composed of a caterer and the unnamed 44P7.2. In terms of its 56 cells, it is the smallest known non-trivial period 21 oscillator, although jam on 44P7.2 (pictured below) has a smaller bounding box.
Despite being composed of two oscillators of smaller periods (3 and 7 respectively), it is considered non-trivial because it has a single cell that is alive in generation 14 and is dead in its other 20 phases.
Image gallery
 Generation 14 reveals the single cell with period 21 (in green) |
 Jam on 44P7.2 with a smaller bounding box of 17×16 RLE: here |
See also
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