Effective nuclear charge on 3p electron of aluminum

Using Slater's rule I calculated the effective nuclear charge on 3p electron of aluminium as:


Config: $\ce{1s^2 (2s^2 2p^6) (3s^2 3p^1)}$


$S = 2(0.35) + 8(0.85) + 2 = 9.5$


$Z\_{eff} = Z - S = 3.5$


The [Wikipedia page](https://en.m.wikipedia.org/wiki/Effective_nuclear_charge#:%7E:text=3p-,4.066,-4.285) states its value as 4.066.


Which one is correct? Did I go wrong somewhere?


