1,tu cac chu so ${1,2,3,4,5,6}$ thiet lap tat ca cac so co 6 chu so khac nhau . Hoi trong cac so da thiet lap duoc co bao nhieu so ma hai chu so ${1 va 6}$ khong dung canh nhau?
2,Tu 7 chu so ${0,1,2,3,4,5,6}$ co the thanh lap duoc bao nhieu so chan, moi so gom 5 chu so khac nhau?