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Baltic Way 2019 number theory
Problem
Does there exist a positive integer such that the first and the second digit of (in decimal notation) are 3 and 9, respectively?
Solution
Yes. Let us observe powers of two of the form . Let be the smallest integer such that ( must exist since is an exponential function and is unbounded from above). From the definition of we know that , therefore . Thus and the first digits of are indeed 3 and 9.
Remark 1. The value of found above is 58 and the respective power of two is .
Remark 2. The smallest power of two satisfying the requirements is .
Remark 1. The value of found above is 58 and the respective power of two is .
Remark 2. The smallest power of two satisfying the requirements is .
Final answer
Yes
Techniques
OtherExponential functionsIntegers