The Pegg Snakes Are Heesch-3 Tiles
The first corona of a tile is a set of tiles congruent to that surrounds . If the first corona exists and can itself be surrounded by a set of tiles congruent to , that is called the second corona, and so on.[more]
A Heesch tile of order is a tile that has a corona of order , but not of order .
The Pegg snake is an infinite sequence of polyiamonds that are each a Heesch tile of order 3. They were found by Ed Pegg Jr and Craig Kaplan, who named them.
This shows that there are infinitely many Heesch tiles of order 3.[less]
 C. S. Kaplan, "Heesch Numbers of Unmarked Polyforms." arxiv.org/abs/2105.09438.