Here's an interactive Ulam spiral with adjustable parameters. http://bl.ocks.org/syntagmatic/5070320 http://bl.ocks.org/syntagmatic/5070320 Open it fullscreen

Here's an interactive Ulam spiral with adjustable parameters. http://bl.ocks.org/syntagmatic/5070320 http://bl.ocks.org/syntagmatic/5070320 Open it fullscreen, lower the size and increase the "max" variable to render more numbers. If you've got a Retina display, the size goes down to 0.5 to take advantage of that. You'll see the long diagonal lines mentioned in the article.