Even Harmonic Waveform

[Martin Czech]

Yes , of course this is possible via  e.g. inverse FFT
or FM (Yamaha has a display of harmonic content in TG77 manual). 

Analog :
A multiplier (ring mod) may do it.
Take a 1kHz sqare

1    3    5    7    9... Khz 

multiply with 1kHz sine from same osc.

gives

0 2  2 4  4 6  6 8  8 10 kHz

add fundamental 1kHz sine from same osc.
there you are :

1 2 4 6 8 10 .... kHz

I can't tell how this looks like in the time domain,
cause this is not defined by the harmonic content allone.

Example : two waves with same harmonic content can have odd
and even symmetry, they look totally different but sound
the same if continously played.

Only if each harmonic is defined in amplitude(t) AND phase(t)
the time domain waveshape will be 100% defined.

m.c.