According to Xmonad/Key codes,
You can also search in
/usr/include/X11/keysymdef.h and lower-case the first character (
Usually (some keyboard configurations differ), the large editing keypad sends symbols such as
XK_KP_0, etc., (the symbols with
_KP_), and pressing NumLock makes the keys send the alternate symbol (such as
XK_0) which is printed on the keyboard.
xterm, for instance, uses that mapping of
XK_KP_xxx to determine what escape sequences to send (this is taken for granted in Why doesn't my keypad work? in the XTerm FAQ).