You forgot `- 2^11` for the surrogate pairs. Gee, why isn't Unicode 2^21 code points? To understand the Unicode code point space you must understand UTF-16. The code space is defined by how UTF-16 works. That was my initial point.
If you're going to count the surrogate pairs as not-a-Unicode-codepoint, you should also count the other noncharacters: the last two codepoints on each of the 17 planes and the range U+FDD0-U+FDEF.
The expansion of Unicode beyond the BMP was designed to facilitate an upgrade compatibility path from UCS-2 systems, but it is extremely incorrect to somehow equate Unicode with UTF-16.
