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John Horton Conway is known for many achievements: Life, the three sporadic groups in the "Conway constellation," surreal numbers, his "Look-and-Say" sequence analysis, the Conway-Schneeberger $15$-theorem, the Free-Will theorem—the list goes on and on.

But he was so prolific that I bet he established many less-celebrated results not so widely known. Here is one: a surprising closed billiard-ball trajectory in a regular tetrahedron:

Q. What are other of Conway's lesser-known results?

John Horton Conway is known for many achievements: Life, the three sporadic groups in the "Conway constellation," surreal numbers, his "Look-and-Say" sequence analysis, the Conway-Schneeberger $15$-theorem, the Free-Will theorem—the list goes on and on.

But he was so prolific that I bet he established many less-celebrated results not so widely known. Here is one: a surprising closed billiard-ball trajectory in a regular tetrahedron:

Q. What are other of Conway's lesser-known results?

Edit: Professor Conway passed away April 11, 2020 from complications of covid-19:

https://www.princeton.edu/news/2020/04/14/mathematician-john-horton-conway-magical-genius-known-inventing-game-life-dies-age

John Horton Conway is known for many achievements: Life, the three sporadic groups in the "Conway constellation," surreal numbers, his "Look-and-Say" sequence analysis, the Conway-Schneeberger $15$-theorem, the Free-Will theorem—the list goes on and on.

But he was so prolific that I bet he established many less-celebrated results not so widely known. Here is one: a surprising closed billiard-ball trajectory in a regular tetrahedron:

Q. What are other of Conway's lesser-known results?

John Horton Conway is known for many achievements: Life, the three sporadic groups in the "Conway constellation," surreal numbers, his "Look-and-Say" sequence analysis, the Conway-Schneeberger $15$-theorem, the Free-Will theorem—the list goes on and on.

But he was so prolific that I bet he established many less-celebrated results not so widely known. Here is one: a surprising closed billiard-ball trajectory in a regular tetrahedron:

Q. What are other of Conway's lesser-known results?