Step 1: Divide the number into separate digits:
8240 => 8 2 4 0
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
8 to 2 = 6
2 to 4 = 2
4 to 0 = 4
0 to 8 = 8
Step 3: Combine the filters to a string:
6 2 4 8 = 6248