Numerous Numerosity 2021 was an online conference dedicated to exploring the concept of number and related notions through diverse disciplines, including computation, complex systems, neuroscience, mathematics, archaeology, physics, and philosophy. The program featured 11 plenary sessions, bringing together influential figures such as Stephen Wolfram, David Krakauer, Karenleigh Overmann, and Nicolas Gisin. Each talk was followed by interdisciplinary discussion spaces with participants, primarily researchers and doctoral students. The event, held from May 24 to 28, 2021, was supported by the Maxwell Institute for Mathematical Sciences at the University of Edinburgh and the Centre for Philosophy and Social Science at the London School of Economics. Over 100 participants from 21 countries attended this international, free-to-access conference. Find all information about Numerous Numerosity 2021 at the event website.