A tree has a
prime labeling and is said to be
prime if there exists a bijection from its vertex
set
to the set
of integers
such that adjacent vertices have coprime labels. Around 1980, Entringer and Tout
conjectured that all trees have a prime labeling, but the conjecture remains open today.
We study Fibonacci trees and prove that a special case (involving the Fibonacci numbers
) of a
conjecture about coprime mappings implies that all Fibonacci trees are prime. We
propose an algorithm for constructing the needed coprime mappings and use it to
show that the first 30 Fibonacci trees are prime, the largest of which has
vertices. This computation also supports the conjecture about
coprime mappings by providing large examples of a coprime mapping
on adjacent sets, the largest of which is on the sets of cardinality
that begin
with
and
,
respectively.
Keywords
prime labelings, coprime mappings, Fibonacci trees