What is the missing number in the following sequence?
$$3,18,90,360,1080,2160,\underline{},0$$

Let's investigate the multiplication values between consecutive positions across the sequence:
* $3\times 6=18$
* $18\times 5=90$
* $90\times 4=360$
* $360\times 3=1080$
* $1080\times 2=2160$

The multiplication factor drops progressively by $1$ at every sequential step ($\times 6,\times 5,\times 4,\times 3,\times 2$). Following this decreasing model, the subsequent multipliers must be $\times 1$ and then $\times 0$:

* $\text{Missing Number}=2160\times 1=2160$
* $\text{Check next step}=2160\times 0=0$ (Matches the final term)

Hence, the missing value is $2160$.