Markov number
A Markov number or Markoff number is a positive integer x, y or z that is part of a solution to the Markov Diophantine equation
studied by Andrey Markoff.
The first few Markov numbers are
1, 2, 5, 13, 29, 34, 89, 169, 194, 233, 433, 610, 985,... Wikipedia