Step 1: Divide the number into separate digits:
86573 => 8 6 5 7 3
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
8 to 6 = 2
6 to 5 = 1
5 to 7 = 2
7 to 3 = 4
3 to 8 = 5
Step 3: Combine the filters to a string:
2 1 2 4 5 = 21245