Let be a prime and be a positive integer, such that has exactly number of digits. Is it true, that between these digits, there will be a digit, which appears minimum times?
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Suppose it is false. Then each digit ( 0 , 1 , 2 , 3 , … , 9 ) appears at most two times. Since there are 1 0 digits and p k has 2 0 digits, each digit appears exactly two times. Hence the digits of the number are 0 , 0 , 1 , 1 , 2 , 2 , 3 , 3 , 4 , 4 , 5 , 5 , 6 , 6 , 7 , 7 , 8 , 8 , 9 , 9 in some order. Note that a power of prime number is only divisible by powers of the same prime number. But p > 3 , so 3 ∣ p k would have to be true, but it is false, because 3 ∣ 0 + 0 + 1 + 1 + 2 + 2 + 3 + 3 + 4 + 4 + 5 + 5 + 6 + 6 + 7 + 7 + 8 + 8 + 9 + 9 = 9 0
So it is true .