Using LaTeX to make circles on an equilateral triangle grid. Seed of Life Coloring Book.

circles.tex

\documentclass[a4paper]{article}
\usepackage{tikz}
\usepackage[left=0cm,top=2cm,right=0cm,bottom=0cm,nohead,nofoot]{geometry}
\usepackage{xcolor} 

\begin{document}

	\begin{tikzpicture}
		\pgfmathsetmacro{\r}{3}
		% Given that A4 paper is 21cm x 29.7 cm, we can calculate the maximum number of circles that will fit on the page based on the radius
        \pgfmathtruncatemacro{\xmax}{21/(\r*1.2)}
        \pgfmathtruncatemacro{\ymax}{\xmax*sqrt(3)/2}

        \foreach \x in {0,...,\xmax-1}
	        \foreach \y in {0,...,\ymax-1} 
			{
				\pgfmathsetmacro{\xorigin}{\x*\r}
				\pgfmathsetmacro{\yorigin}{\y*\r*sqrt(3)}
				\pgfmathsetmacro{\xoffset}{\r*(\x+0.5)}
				\pgfmathsetmacro{\yoffset}{(2*\y+1)*sqrt(3)*\r/2}
				% Fading color depending on position!
				% \pgfmathsetmacro{\c}{(\x+\y)/(\xmax+\ymax)}
				% \definecolor{tracecolor}{rgb}{\c,\c,\c}
				\draw[color=black] (\xorigin,\yorigin) circle [radius=\r cm];
				\draw[color=black] (\xoffset, \yoffset) circle [radius=\r cm];
			}
	
	\end{tikzpicture}

\end{document}