Four-digit numbers can look simple until order starts to matter. Take 1234. Rearranging those four digits can create many different sequences: 1243, 1324, 2143, 4321, and so on. Now compare that with 1123. Because two digits are identical, swapping the two 1s does not create a visibly new number. That reduces the number of distinct …
Why Repeated Digits Change 4D Permutations A Practical Number Guide for KoinToto Readers

