Step 1: Divide the number into separate digits:
58021 => 5 8 0 2 1
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
5 to 8 = 3
8 to 0 = 8
0 to 2 = 2
2 to 1 = 1
1 to 5 = 4
Step 3: Combine the filters to a string:
3 8 2 1 4 = 38214