number of bits in bent funtion

[Sandy Harris]

Is there a general rule for the number of set
bits in a bent boolean function of n input bits?

I know from the Mister and Adams paper at SAC 96:
http://adonis.ee.queensu.ca:8000/sac/sac96/papers.html
that any 8-bit bent function has either 120 or 136 bits
set. That's (2^8)/2 +- 8.

Does that generalise to (2^n)/2 +- n for any even n?
Or is there some other general rule?