The function reverses the input string and appends the length of the string minus 1 to the end of the reversed string.

[CODE]:
```python
def approx_function(s):
    return s[::-1] + str(len(s) - 1)
```

Let me run more tests to confirm this hypothesis.
COMMAND: PYTHON(./temp/function.py "abc" "123" "pythonista" "testing" "example123")