Step 1: Divide the number into separate digits:
29581 => 2 9 5 8 1
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
2 to 9 = 7
9 to 5 = 4
5 to 8 = 3
8 to 1 = 7
1 to 2 = 1
Step 3: Combine the filters to a string:
7 4 3 7 1 = 74371