Step 1: Divide the number into separate digits:
7041 => 7 0 4 1
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
7 to 0 = 7
0 to 4 = 4
4 to 1 = 3
1 to 7 = 6
Step 3: Combine the filters to a string:
7 4 3 6 = 7436