Step 1: Divide the number into separate digits:
15782 => 1 5 7 8 2
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
1 to 5 = 4
5 to 7 = 2
7 to 8 = 1
8 to 2 = 6
2 to 1 = 1
Step 3: Combine the filters to a string:
4 2 1 6 1 = 42161