Step 1: Divide the number into separate digits:
06518 => 0 6 5 1 8
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
0 to 6 = 6
6 to 5 = 1
5 to 1 = 4
1 to 8 = 7
8 to 0 = 8
Step 3: Combine the filters to a string:
6 1 4 7 8 = 61478