Step 1: Divide the number into separate digits:
54906 => 5 4 9 0 6
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
5 to 4 = 1
4 to 9 = 5
9 to 0 = 9
0 to 6 = 6
6 to 5 = 1
Step 3: Combine the filters to a string:
1 5 9 6 1 = 15961