As character names:

U+FDD9 <not a character> character (&#xFDD9;)

As raw characters:

As a string of HTML entities:

&#xfdd9;

Decoder output:

Byte number 1 is decimal 240, hex 0xF0, octal \360, binary 11110000
This is the first byte of a 4 byte sequence.

Byte number 2 is decimal 143, hex 0x8F, octal \217, binary 10001111
This is continuation byte 1, expecting 2 more.

Byte number 3 is decimal 183, hex 0xB7, octal \267, binary 10110111
This is continuation byte 2, expecting 1 more.

Byte number 4 is decimal 153, hex 0x99, octal \231, binary 10011001
This is continuation byte 3, expecting 0 more.

U+FDD9	<not a character>