@christianp I've seen applications where subscripts were added to \(\pi\) to denote a constant not quite related to the circle; would that count?
@christianp http://www.m-hikari.com/ams/ams-2012/ams-121-124-2012/elgindiAMS121-124-2012.pdf was one of the papers I had in mind, where for a real \(p\), there is an associated version of \(\sin\), \(\cos\), and \(\pi\). (The usual ones correspond to \(p=2\).)
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