Batch conversion of xlsx files to txt in Python

Question

I am trying to convert files with the extension xlxs to txt files. All items have the same name and are marked with a number. The problem is that there are no numbers in sequence but there are gaps. I have tried structuring the code but it crashes after the first line.

import numpy as np
import pandas as pd

for i in range (1,317,1):
    try:
        df = pd.read_excel(r'D:\Tesi\VAIA\Algoritmo\Tri_%i.xlsx' %i, sheet_name='Tri_%i' %i)
        with open(r'D:\Tesi\VAIA\Algoritmo\Nuvole_split\Nuvola%i.txt' %i, 'w') as outfile:
                df.to_string(outfile)
    except Exception:
        pass

There may be 317 possible output files, but in practice I only have 40. Numbered in ascending order I know that there are: 2, 6, 9, 26 .... . So I'm setting up a loop to open and convert them but it crashes after converting the one in position 2. Any suggestions?