Count

Number of digits in $n = \left\lfloor \log _{ 10 }{ n } \right\rfloor +1$ .

So the digits are

$\Rightarrow \left\lfloor \log { { 3 }^{ 43 } } \right\rfloor +1\\ \Rightarrow \left\lfloor 43\log { 3 } \right\rfloor +1\\ \log { 3 } \approx 0.4771\\ \Rightarrow \left\lfloor 20.52 \right\rfloor +1\\ \Rightarrow 21$