The mythical tree problem is a combinatorial problem created by Harvey Friedman.
In the problem, the tree has a strange growth pattern. In the first stage, the tree grows k branches, forming k treetops. In the next stage, one of the treetops forms k+1 branches, increasing the number of treetops. The problem asks: what is the maximum number of branch segments a tree starting at k branches grow at once, during the tree's final stage of growth, provided that a squirrel can go from the root to any treetop without navigating more than four branch segments?
Friedman has shown that:
- k = 2 corresponds to 22,539,988,369,406 segments (there was a misprint in his work: there are exactly 41*239 - 2 branch segments, not 40*239 - 2)
- k = 3 corresponds to a value > 2295
- k = 4 corresponds to a value > 2 ↑↑ 2295
- The growth rate of the number of segments as a function of k can be generalized to be similar to that of the Ackermann function.