Kempner function

The Kempner function, often denoted as \( K(n) \), is a function defined in number theory that counts the number of positive integers up to \( n \) that are relatively prime to \( n \) and also which contain no digit equal to 0 when expressed in decimal notation. This function is named after mathematician Howard Kempner. More formally, the Kempner function can be defined as follows: - Let \( n \) be a positive integer.