Formula for Mercuric Carbide: Hg^2C_{2}?

[GLprincess02]

One of my homework questions asks to give the formula for the compound mercuric carbide. I'm pretty sure that the symbol for mercuric is $$Hg^2$$ and the symbol for carbide is $$C_{2}$$, so does this make the formula $$Hg^2C_{2}$$?? Or is it more complicated than that?

 

[chemisttree]

sounds good to me but lose the superscript '2'.