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|Number of cells||16|
|Rotor type||Diagonal on-off|
|Year of discovery||Unknown|
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21P2 is about the thirty-eighth most common naturally-occurring oscillator in Achim Flammenkamp's census, being less common than boat on spark coil and block on griddle, about as common as the fore and back, and more common than trans-block on long hook eating tub and trans-beacon down on long hook.
- Achim Flammenkamp (September 7, 2004). "Most seen natural occurring ash objects in Game of Life". Retrieved on January 15, 2009.
- 16P2.91 at Heinrich Koenig's Game of Life Object Catalogs