I have an unbalanced data of 3000 firms over 30 years. I am trying to run a regression with firm and year fixed effects and two way clustering across firms and years. I am trying the following commands. Is this the correct way to estimate?

1) xi: xtivreg2 Y x1 x2 x3, fe cluster( firmID Year)

or

2) xi: xtivreg2 Y x1 x2 x3 i.year, fe cluster( firmID Year)

Also, it gives me centered and uncentered R2. Which one of them is equivalent to the adjusted-R2?
Finally, there is NO constant in the output. Why is that?