Rn: [Xe] 4f15 5d10 6s2 6p6?
That would just be the wrong number of electrons. You can only fit 14 into 4f.
La has 4f
0, Lu has 4f
14.
Periodic tables vary; some have La below Y (in the d block) with Ce-Lu separate, as the f block, while some have La-Yb separate, with Lu below Y (then all the 3rd row transition metals have 4f
14). Some, like
www.ptable.com, have La-Lu separate, illogically suggesting a 15-element f block. I prefer the first style.