Outermost electronic configuration of f block elements

Why is it $(n-2)\mathrm{f}^{1-14}(n-1)\mathrm{d}^{0-1}n\mathrm{s}^2$. 


The only exception I thought to this formula was Thorium $\ce{5f^{0} 6d^{2} 7s^{2}}$.


So I feel it should be $(n-2)\mathrm{f}^{1-14}(n-1)\mathrm{d}^{0-2}n\mathrm{s}^2$.




As you said, if you look at the electron configurations of [Lanthanides](http://chemwiki.ucdavis.edu/Inorganic_Chemistry/Descriptive_Chemistry/f-Block_Elements/The_Lanthanides#Electron_Configuration) and [Actinides](http://chemwiki.ucdavis.edu/Inorganic_Chemistry/Descriptive_Chemistry/f-Block_Elements/The_Actinides#Actinide_Properties_Table), Thorium seems to be the only exception from this empirical rule. You could expand the rule to also include the case of Thorium but I would say it is more useful to have the rule describe the majority of cases and remember $\ce{Th}$ as an exception.


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