What is:

$$\\\sqrt{\sqrt[{\sqrt[-1]{2}^\sqrt{9}}]{6}}\\\\$$

I do not think that this has any definative meaning  

i think it a image number not sure 

The answer is 1296

You need to show your working Einstein :/

$$\sqrt[-1]{2}$$     I can guess at what it might mean but I have never seen an expression like this before !

You can verify by yourself, sqrt(sqrt(6,sqrt(2,-1)^sqrt(9)))=1296

I want you to verify it by hand. :)

$$\sqrt{\sqrt[{\sqrt[-1]{2}^\sqrt{9}}]{6}}\\ =\sqrt{\sqrt[{\sqrt[-1]{2}^3}]{6}}\\ =\sqrt{\sqrt[\left ( \frac{1}{2} \right )^3]{6}}\\ =\sqrt{\sqrt[\frac{1}{8}]{6}}\\ =\sqrt{1679616} =1296$$