Step 1: Divide the number into separate digits:
7941 => 7 9 4 1
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
7 to 9 = 2
9 to 4 = 5
4 to 1 = 3
1 to 7 = 6
Step 3: Combine the filters to a string:
2 5 3 6 = 2536