Step 1: Divide the number into separate digits:
1204 => 1 2 0 4
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
1 to 2 = 1
2 to 0 = 2
0 to 4 = 4
4 to 1 = 3
Step 3: Combine the filters to a string:
1 2 4 3 = 1243