Power of 2017

Let 3 < p 3<p be a prime and k k be a positive integer, such that p k p^k has exactly 20 20 number of digits. Is it true, that between these 20 20 digits, there will be a digit, which appears minimum 3 3 times?

Yes, it is true No, it is false

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1 solution

Suppose it is false. Then each digit ( 0 , 1 , 2 , 3 , , 9 0, 1, 2, 3, \dots, 9 ) appears at most two times. Since there are 10 10 digits and p k p^k has 20 20 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 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 p>3 , so 3 ∤ p k 3\not\mid 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 = 90 3\mid 0+0+1+1+2+2+3+3+4+4+5+5+6+6+7+7+8+8+9+9=90

So it is true \boxed{\text{true}} .

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