222 ( vi ta lay 99 cong 123 )

Hoac : 123 co 122 khoang cach va lay so nay cong cho 100

*** Ta co quy luat muon tim 1 so dung thu bao nhieu thi lay so thu tu cua so do cong cho 99 hoc lay khoang cach so do cong 100

Luu y : muon tim khoang cach ta lay so thu tu tru di 1