\(81=3^4\rightarrow\text{Có: }4+1=5\text{(ước)}\)
\(250=2.5^3\rightarrow\text{Có:}\left(1+1\right).\left(3+1\right)=2.4=8\left(ước\right)\)
\(126=2.3^2.7\rightarrow\text{Có:}\left(1+1\right).\left(2+1\right).\left(1+1\right)=2.3.2=12\left(\text{ước}\right)\)