Problem #PRU-73739

Problems Number Theory Numeral systems Decimal number system Algebra Exponential functions and logarithms Exponential inequalities

Problem

Let’s call a natural number good if in its decimal record we have the numbers 1, 9, 7, 3 in succession, and bad if otherwise. (For example, the number 197,639,917 is bad and the number 116,519,732 is good.) Prove that there exists a positive integer \(n\) such that among all \(n\)-digit numbers (from \(10^{n-1}\) to \(10^{n-1}\)) there are more good than bad numbers.

Try to find the smallest possible \(n\).