Step 1: Divide the number into separate digits:
5042 => 5 0 4 2
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
5 to 0 = 5
0 to 4 = 4
4 to 2 = 2
2 to 5 = 3
Step 3: Combine the filters to a string:
5 4 2 3 = 5423