Попробуйте это,
import re
with open('file1.txt', 'r') as f:
data = f.read()
list_of_numbers = re.findall(r'(?:[\d]+)',data)
list_of_numbers = map(int, list_of_numbers)
print(max(list_of_numbers))
Выход:
73905 # max number
your list_of_numbers look like this
['15', '5', '46', '8', '9', '214', '8', '365', '67', '2', '3', '3', '5', '1',
'8', '22', '6', '3', '24', '46', '2219', '07', '30', '8', '3', '2', '283', '68',
'86', '6', '7', '4', '84', '73905', '3', '71', '985', '54', '32', '8', '23', '7',
'9', '575', '9', '7', '0', '99', '2', '5', '33', '6', '76', '8']