1 to 50 is divided into seven categories: 1, 2, 3, 4, 5, 6 and divisible by 7, and the rest 1 is {1, 8, 15, 22, 29, 36, 43. After classification in turn, elements with meaning greater than 1 and elements with meaning greater than 6 cannot coexist. Similarly, elements above 2 and 5 cannot coexist, and elements above 3 and 4 cannot coexist. There can only be one element at most, so there are at most eight elements greater than 1, one is 2 or 5, the other is 3 or 4, and the other is divisible.