Step 1: Divide the number into separate digits:
7105 => 7 1 0 5
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
7 to 1 = 6
1 to 0 = 1
0 to 5 = 5
5 to 7 = 2
Step 3: Combine the filters to a string:
6 1 5 2 = 6152