Step 1: Divide the number into separate digits:
26618 => 2 6 6 1 8
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
2 to 6 = 4
6 to 6 = 0
6 to 1 = 5
1 to 8 = 7
8 to 2 = 6
Step 3: Combine the filters to a string:
4 0 5 7 6 = 40576