7 is double the last number and subtract from the rest749 (easily divisible by 7 but for example sake)9*2=1874-18=566*2=125-12= -7, or if you recognize 56 is 7*8...I'll do another, random 6 digit number appear!592711*2=25927-2=59255*2=10592-10=5822*2=458-4=54, or not divisible I guess for this to work you should at least know the first 10 times tables...