Step 1: Divide the number into separate digits:
2401 => 2 4 0 1
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
2 to 4 = 2
4 to 0 = 4
0 to 1 = 1
1 to 2 = 1
Step 3: Combine the filters to a string:
2 4 1 1 = 2411