On one Thursday evening (never could get hang of Thursdays), I ran into a thread that John Carlos Baez posted in Mastodon about Lemniscate constant, the “evil twin” of π (pi).
It’s symbol is ϖ.
Wikipedia article starts with quite a kick ass description:
In mathematics, the lemniscate constant ϖ is a transcendental mathematical constant that is the ratio of the perimeter of Bernoulli’s lemniscate to its diameter, analogous to the definition of π for the circle.
I don’t claim to understand any of that, other than the “π for the circle” part but it sounds rad.