As character names:

U+4FFFF <not a character> character (&#x4FFFF;)

As raw characters:

񏿿

As a string of HTML entities:

&#x4ffff;

Decoder output:

Byte number 1 is decimal 241, hex 0xF1, octal \361, binary 11110001
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 191, hex 0xBF, octal \277, binary 10111111
This is continuation byte 2, expecting 1 more.

Byte number 4 is decimal 191, hex 0xBF, octal \277, binary 10111111
This is continuation byte 3, expecting 0 more.

U+4FFFF	<not a character>