Step 1: Divide the number into separate digits:
02148 => 0 2 1 4 8
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
0 to 2 = 2
2 to 1 = 1
1 to 4 = 3
4 to 8 = 4
8 to 0 = 8
Step 3: Combine the filters to a string:
2 1 3 4 8 = 21348