The escapes that ‘-printf’ and ‘-fprintf’ recognise are:
\a
Alarm bell.
\b
Backspace.
\c
Stop printing from this format immediately and flush the output.
\f
Form feed.
\n
Newline.
\r
Carriage return.
\t
Horizontal tab.
\v
Vertical tab.
\\
A literal backslash (‘\’).
\0
ASCII NUL.
\NNN
The character whose ASCII code is NNN (octal).
A ‘\’ character followed by any other character is treated as an ordinary character, so they both are printed, and a warning message is printed to the standard error output (because it was probably a typo).