Pentadecathlon (or PD; plural pentadecathlons[note 1]) is a period 15 oscillator that was found in 1970 by John Conway while tracking the history of short rows of cells (see one-cell-thick pattern); indeed, 10 cells placed in a row evolve into this object. It is the only known oscillator that is a polyomino in more than one phase (besides the blinker).
Pentadecathlon is the most natural oscillator of period greater than 3 (and indeed, the second most natural oscillator of period greater than 2) in Achim Flammenkamp's census. In fact, it is the fifth or sixth most common oscillator overall in this census, being about as frequent as the clock, but much less frequent than the blinker, toad, beacon or pulsar. The pentadecathlon is also the fifty-second most common object on Adam P. Goucher's Catagolue and by far the most common period 15 oscillator, with all other natural oscillators of that period featuring it combined with some other object.
Uses of the pentadecathlon
The pentadecathlon is so called because it has a period of 15 generations. This, being a factor of 30, means that it can be elegantly used in combination with period 30 devices (based on the queen bee shuttle). Firstly, it can reflect a glider 180° as in p60 glider shuttle, and a pair of perpendicular pentadecathlons can rotate a glider 90°.
The pentadecathlon is classified as a pulsating oscillator, since it undulates throughout its cycle. During this process, the pentadecathlon throws off multiple accessible sparks. More specifically, the oscillator produces horizontal T-nose sparks, horizontal V sparks and vertical domino sparks. Two copies of these domino sparks can be used to hassle toads in two distinct ways. The V sparks elegantly convert blocks into gliders, which forms the basis of the p30 *WSS => glider converter and aforementioned glider reflectors. This property is also exploited in numerous oscillators.
- In EightLife, it still functions as a period 15 oscillator, but it generates extra internal sparks.
- ↑ The correct Ancient Greek dual and plural forms, pentadecathlo and pentadecathla, are not in common use.
- 12P15.1 at Heinrich Koenig's Game of Life Object Catalogs