Step 1: Divide the number into separate digits:
79409 => 7 9 4 0 9
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 0 = 4
0 to 9 = 9
9 to 7 = 2
Step 3: Combine the filters to a string:
2 5 4 9 2 = 25492