@Ben N @ https://superuser.com/questions/1024948/windows-10-alt-code-results-in-wrong-character#answer-1024956:
By default, the numeric keypad way of entering characters by code can only access the first 256 characters. (I believe these are defined by your system's code page for non-Unicode programs.) Codes bigger than 256 get wrapped around, so code 257 actually gets you character 1.

To enable the entry of all Unicode characters by code, create a string registry value in Computer\HKEY_CURRENT_USER\Control Panel\Input Method called EnableHexNumpad with the value of 1. Then you'll be able to enter any character by holding down the right Alt key, pressing the + button on the numeric keypad, entering the hex code (2, 7, 1, 3 in your case), and releasing the Alt key. You may need to log off and back on before this input type is enabled.

Note that the non-+ method of entering ASCII characters by code will continue to wrap around even after you enable this mode.