Cyrillic Capital Letter Soft Em
HTML Entity Browser Test:

U+A666 is the Unicode hex value of the character Cyrillic Capital Letter Soft Em, which is categorized as "uppercase letter" in the Unicode 6.0 character table.

Unicode Character Information
Unicode Hex U+A666
Character Name CYRILLIC CAPITAL LETTER SOFT EM
General Category Uppercase Letter [Code: Lu]
Canonical Combining Class 0
Bidirectional Category L
Mirrored N
Lowercase Version U+A667
Unicode Character Encodings
Cyrillic Capital Letter Soft Em HTML Entity Ꙧ (decimal entity), Ꙧ (hex entity)
Windows Key Code Alt 42598 or Alt +A6661
Programming Source Code Encodings Python hex: u"\uA666", Hex for C++ and Java: "\uA666"
UTF-8 Hexadecimal Encoding 0xEA99A6
1 To type a Unicode symbol in Windows, hold down the ALT key and enter the decimal or hexadecimal code provided using the numeric keypad. The decimal alt code (Alt 42598) will only work on computers with support for this Unicode character in the active code page. The hexadecimal alt code (Alt +A666) will work for all Unicode characters provided Hex input from the numeric keypad is enabled.
* If the Cyrillic Capital Letter Soft Em character does not display correctly in your browser, you may not have a Unicode font on your system that supports this particular symbol.