 = 18 . Since then , only five more of these values have been found . In the same 1955 paper , Greenwood and Gleason also computed the multicolor Ramsey number R ( 3 @,@ 3 @,@ 3 ) : the smallest number r such that , if a complete graph on r vertices has its edges colored with three colors , then it necessarily contains a monochromatic triangle . As they showed , R ( 3 @,@ 3 @,@ 3 ) = 
