This article is from the ZTerm FAQ, by Les Jones firstname.lastname@example.org with numerous contributions by others.
The numeric keypad is sometimes used for special editing functions
on the host machine. If you want to use the numeric keypad for PF
keys, make sure VT100 Keypad is turned on. Conversely, if you
always want to use it for entering numbers, turn off the "VT100
Keypad" option in the Terminal dialog for that service.