Step 1: Divide the number into separate digits:
8624 => 8 6 2 4
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
8 to 6 = 2
6 to 2 = 4
2 to 4 = 2
4 to 8 = 4
Step 3: Combine the filters to a string:
2 4 2 4 = 2424