Step 1: Divide the number into separate digits:
5064 => 5 0 6 4
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
5 to 0 = 5
0 to 6 = 6
6 to 4 = 2
4 to 5 = 1
Step 3: Combine the filters to a string:
5 6 2 1 = 5621