If you have already tried to use the keypad with putty to write numbers in vi, vim, nano, etc., you must have seen that it did not work.
To solve this problem, just change some putty settings.

To begin, go to "Terminal -> Features" and check the "Disable application keypad mode" box.

Then, for the "The Function keys and Keypad" option, simply select "Linux".

Finally, select the "Default Settings" session and click "Save".

Now, the numeric keypad will work correctly in vi, vim, ...