Step 1: Divide the number into separate digits:
91049 => 9 1 0 4 9
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
9 to 1 = 8
1 to 0 = 1
0 to 4 = 4
4 to 9 = 5
9 to 9 = 0
Step 3: Combine the filters to a string:
8 1 4 5 0 = 81450