Kaprekar's constant is equal to 6174, named after discoverer D. R. Kaprekar. The number arises in analysis of the following function: given a four-digit positive integer \(n\), let \(a\) be the number formed by sorting \(n\)'s digits in ascending order, and let \(d\) be the number formed by sorting the digits in descending order (adding trailing zeroes so that \(d\) has 4 digits). We now define \(K(n) = d - a\). Kaprekar has shown that, if we start with any 4-digit number other than a multiple of 1111, then repeated application of the \(K\) will eventually reach the fixed point 6174 within seven steps.