1 files changed, 76 insertions, 0 deletions
diff --git a/ulam-triangular.tex b/ulam-triangular.tex
new file mode 100644
index 0000000..8e4e0e1
--- /dev/null
+++ b/ulam-triangular.tex
@@ -0,0 +1,76 @@
+    \documentclass[border=10cm]{standalone}
+    
+    \usepackage{pgf}
+    
+    \newcount\ulami
+    \newcount\ulamj
+    \newcount\ulamlen
+    
+    \newcount\ulamx
+    \newcount\ulamy
+    \newcount\ulamdx
+    \newcount\ulamdy
+    
+    \ulami=1 %
+    \ulamj=0 %
+    \ulamlen=1 %
+    \ulamdx=-1 %
+    \ulamdy=1 %
+    \ulamx=0 %
+    \ulamy=0 %
+    
+    \def\ulamplot#1{%
+      \advance\ulami by 1 %
+      \advance\ulamj by 1 %
+    
+      \advance\ulamx by \the\ulamdx %
+      \advance\ulamy by \the\ulamdy %
+    
+      \pgfpathmoveto{\pgfpoint{\the\ulamx cm}{\the\ulamy cm}}
+    
+      \pgfmathparse{isprime(\the\ulami)}
+      \let\r=\pgfmathresult
+      \ifnum\r=1
+        \pgfpathcircle{\pgfpoint{\the\ulamx cm}{\the\ulamy cm}}{5pt}
+      \fi
+    
+      \ifnum\ulamj=\the\ulamlen %
+        \advance\ulamlen by 1 %
+        \ulamj=0 %
+        \ifnum\ulamdx=1 %
+          \ulamdx=-1 %
+          \ulamdy=1 %
+        \else%
+          \ifnum\ulamdx=-1 %
+            \ulamdx=0 %
+            \ulamdy=-1 %
+          \else%
+            \ulamdx=1 %
+            \ulamdy=0 %
+          \fi
+        \fi
+      \fi
+    
+      \ifnum#1>0 %
+        \advance#1 by -1 %
+        \ulamplot{#1}%
+      \fi
+    }
+    
+    \begin{document}
+    
+    \begin{pgfpicture}
+      \pgfmathsetmacro{\x}{cos(60)}
+      \pgfmathsetmacro{\y}{sin(60)}
+      \pgftransformcm{1}{0}{\x}{\y}{\pgfpointorigin}
+    
+      \pgfpathmoveto{\pgfpointorigin}
+      \color{blue}
+      \newcount\ulamn
+      \ulamn=400
+      \ulamplot{\ulamn}
+      \pgfusepath{stroke,fill}
+    \end{pgfpicture}
+    
+    \end{document}
+