Template:Selected anniversaries/October 21
From Gnomon Chronicles
1914: Mathematics and science writer Martin Gardner born. His interests will include stage magic, scientific skepticism, philosophy, religion, and literature.
1969: Mathematician and academic Wacław Sierpiński dies. He made important contributions to set theory (research on the axiom of choice and the continuum hypothesis), number theory, theory of functions, and topology.
2017: Green Spiral 9 feels more green than ever, according to new chromatographic analysis.