Step 1: Divide the number into separate digits:
6584 => 6 5 8 4
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
6 to 5 = 1
5 to 8 = 3
8 to 4 = 4
4 to 6 = 2
Step 3: Combine the filters to a string:
1 3 4 2 = 1342