Step 1: Divide the number into separate digits:
7621 => 7 6 2 1
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
7 to 6 = 1
6 to 2 = 4
2 to 1 = 1
1 to 7 = 6
Step 3: Combine the filters to a string:
1 4 1 6 = 1416