CIRCLE WITH A DOT

@johncarlosbaez On Gro-Tsen's question "Why 13?": I vaguely remember the number 13 to be symbolic in meso-American culture, a bit like 7 in Europe. At least, there is a 13 day cycle, the trecena https://en.wikipedia.org/wiki/Trecena?wprov=sfla1, used in many meso-American calendars. It was used by Mayas in the Tzol'kin, alongside the long count