exponential with complex exponents



I'm attempting to get numerical results by using the "float" function.  I'm 
not real clear on how it is supposed to work and the results I'm getting 
confuse me even more.

(%i2) float(%e^(2/3*%pi*%i));
(%o2) .8660254037844386*%i-0.5
(%i3) float(%e^(10/21*%pi*%i));
(%o3) 2.718281828459045^(10*%i*%pi/21)

Why does %o2 turn out to be written directly as a complex number, but %o3 not 
get simplified at all?  Is there another function I should be using rather 
than "float"?  I want the expressions simplified to be written as a complex 
number like %o2.

Thanks
Joel

Version information is:
Maxima version: 5.9.3
Maxima build date: 13:23 9/11/2006
host type: i686-pc-linux-gnu
lisp-implementation-type: CLISP
lisp-implementation-version: 2.38 (2006-01-24) (built 3366983146) (memory 
3366984204)