Step 1: Divide the number into separate digits:
73178 => 7 3 1 7 8
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 7 = 6
7 to 8 = 1
8 to 7 = 1
Step 3: Combine the filters to a string:
4 2 6 1 1 = 42611