One more Tur\'an number and Ramsey number for the loose 3-uniform path of length three

Abstract

Let $P$ denote a 3-uniform hypergraph consisting of 7 vertices $a,b,c,d,e,f,g$ and 3 edges $\{a,b,c\}, \{c,d,e\},$ and $\{e,f,g\}$. It is known that the $r$-color Ramsey number for $P$ is $R(P;r)=r+6$ for $r\le 9$. The proof of this result relies on a careful analysis of the Tur\'an numbers for $P$. In this paper, we refine this analysis further and compute the fifth order Tur\'an number for $P$, for all $n$. Using this number for $n=16$, we confirm the formula $R(P;10)=16$.