Step 1: Divide the number into separate digits:
5556 => 5 5 5 6
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
5 to 5 = 0
5 to 5 = 0
5 to 6 = 1
6 to 5 = 1
Step 3: Combine the filters to a string:
0 0 1 1 = 0011