number of bits in bent funtion

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?