Espiral de Ulam usando TikZ

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{math}
\usepackage{ifthen}
\usepackage[active,tightpage]{preview}
\PreviewEnvironment{tikzpicture}
\setlength\PreviewBorder{0.125pt}
%
% File name: Ulam-spiral.tex
% Description: 
% The Ulam spiral is shown.
% 
% Date of creation: October, 21st, 2023.
% Date of last modification: October, 21st, 2023.
% Author: Efraín Soto Apolinar.
% https://www.aprendematematicas.org.mx/author/efrain-soto-apolinar/instructing-courses/
%
% Terms of use:
% https://creativecommons.org/licenses/by-nc-sa/4.0/
% Your commitment to the terms of use is greatly appreciated.
%
\begin{document}
	%
	\begin{tikzpicture}
		\pgfmathsetmacro{\l}{50} % length of the side of the square
		\pgfmathsetmacro{\n}{\l * \l}	% number of terms
		\pgfmathsetmacro{\m}{int(\n - 1)}
		%
		\draw[fill=red!15] (0,0) rectangle (1,1) node[gray,shift=({(-0.5,-0.5)})] {$1$};
		%
		\foreach \i [remember=\x as \xlast (initially 0), remember=\y as \ylast (initially 0),
			remember=\dx as \dxlast (initially 0), remember=\dy as \dylast (initially -1)] in {1,2,...,\m}{
			\tikzmath{\x = \xlast; \y = \ylast; \dx = \dxlast; \dy = \dylast;}
			\pgfmathsetmacro{\j}{int(\i + 1)}
			\pgfmathsetmacro{\d}{or(or(\x == \y, and(\x < 0, \x == -\y)), or(and(\x < 0, \x == -\y), and(\x > 0, \x == 1 - \y)))}
			% To compute location
			\ifthenelse{\d=1}{
				\pgfmathsetmacro{\t}{\dx}
				\pgfmathsetmacro{\dx}{-\dy}
				\pgfmathsetmacro{\dy}{\t}
			}{}
			% Location of the current term
			\pgfmathsetmacro{\x}{\xlast + \dx}
			\pgfmathsetmacro{\y}{\ylast + \dy}
			\pgfmathsetmacro{\primality}{isprime(\j)}
			%
			\ifthenelse{\primality=1}{
				\draw[fill=cyan!25,shift={(\x,\y)}] (0,0) rectangle (1,1) node[shift=({(-0.5,-0.5)})] {$\j$};
			}{
				\draw[fill=gray!15,shift={(\x,\y)}] (0,0) rectangle (1,1) node[gray,shift=({(-0.5,-0.5)})] {$\j$};
			}
		}
		%
	\end{tikzpicture}
	%
\end{document}