Step 1: Divide the number into separate digits:
7639 => 7 6 3 9
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
7 to 6 = 1
6 to 3 = 3
3 to 9 = 6
9 to 7 = 2
Step 3: Combine the filters to a string:
1 3 6 2 = 1362