235らしい。By Haskell君

parts = sort [a*b*c*d*e*f*g*h | a<-[1,2],b<-[1,3],c<-[1,4],d<-[1,5],e<-[1,6],f<-[1,7],g<-[1,8],h<-[1,9]]
isNotSum x = (==Nothing) $ find (==x) [a+b|a<-parts,b<-parts]
head [x|x<-[2..],isNotSum x]