Step 1: Divide the number into separate digits:
73107 => 7 3 1 0 7
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
7 to 3 = 4
3 to 1 = 2
1 to 0 = 1
0 to 7 = 7
7 to 7 = 0
Step 3: Combine the filters to a string:
4 2 1 7 0 = 42170