Modular exponentiation on calculator for textbook RSA How do you encrypt $51$ with public key $(n,e) = (91,23)$

I understand that $c = 51^{23} \bmod 91$.  How can I calculate the result on a calculator?
If your calculator is able to compute $n^2$, you can compute $m^e \bmod n$ using the binary exponential method.

In this method, you should first compute the binary form of $e$. Let $\ell$ be the number of bits in $e$, and let $e_i$ denote the $i$-th bit of $e$, so that $e=\sum\limits_{i=0}^\ell e_i \cdot 2^i$.

Now, with the algorithm below, you can compute $c$:


  $z:=1$
  $\text{for } i:= \ell \text{ down to } 0 \text{ do:}$
  $\quad z:=z^2 \bmod n$
  $\quad \text{if } e_i = 1 \text{ then } z:=(z \cdot m) \bmod n$
  $\text{end for}$
  $\text{return } z$