On some three-color Ramsey numbers for paths

Abstract

For graphs G1,G2,G3, the three-color Ramsey number R(G1,G2,G3) is the smallest integer n such that if we arbitrarily color the edges of the complete graph of order n with 3 colors, then it contains a monochromatic copy of Gi in color i, for some 1≤i≤3.First, we prove that the conjectured equality R(C2n,C2n,C2n)=4n, if true, implies that R(P2n+1,P2n+1,P2n+1)=4n+1 for all n≥3. We also obtain two new exact values R(P8,P8,P8)=14 and R(P9,P9,P9)=17, furthermore we do so without help of computer algorithms. Our results agree with a formula R(Pn,Pn,Pn)=2n−2+(nmod2) which was proved for sufficiently large n by Gyárfás, Ruszinkó, Sárközy, and Szemerédi (2007). This provides more evidence for the conjecture that the latter holds for all n≥1.