Step 1: Divide the number into separate digits:
29404 => 2 9 4 0 4
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
2 to 9 = 7
9 to 4 = 5
4 to 0 = 4
0 to 4 = 4
4 to 2 = 2
Step 3: Combine the filters to a string:
7 5 4 4 2 = 75442