According to this reference:
Chapter 4: Configuring PuTTY | PuTTY User Manual (putty-0.68-manual)
Quote:
In SCO mode, the function keys F1 to F12 generate ESC [M through to ESC [X. Together with shift, they generate ESC [Y through to ESC [j. With control they generate ESC [k through to ESC [v, and with shift and control together they generate ESC [w through to ESC [{.
If you don't know what any of this means, you probably don't need to fiddle with it.