I found more complexed pattern. Unfortunately, it passed only these initial 5 test cases, no further. Such a shame and loss of time. What could be the chances for that. So...

If the number has even number of digits:

3479283469 => 34792 | 83469 => sum A | sum B => sum B - sum A => 30 - 25 => 5

123321 => 123 | 321 => sum A | sum B => sum B - sum A => 6 - 6 => 0

If the number has odd number of digits:

90783 => 9 | 0783 => count of digits smaller than first digit => 4

300 => 3 | 00 => count of digits smaller than first digit => 2

89282350306 => 8 | 9282350306 => count of digits smaller than first digit => 8