Advertising with Slate Star Codex is a good way to reach people in a high-openness-to-experience and mathematically-inclined demographic.
Advertisements will show up on the sidebar of the blog in a 360×120 tower format. You can either design your own, or have one designed for you to fit the style of the rest of the blog. Some examples of previous advertisements:
An advertisement costs $250/month or $1250/6 months. Ads can expect about 10,000 to 20,000 impressions per day. Past ads that were interesting and well-targeted have gotten about five hundred clickthroughs in their first week, followed by a steady fifty clickthroughs per week thereafter.
If interested, email scott[at]shireroth[dot]org.
Disclaimer: Ad purchases will not be refunded if this blog stops publishing on a regular schedule, but this has never happened. If there are many ads at the same time, they will all be included, and will be cycled from top to bottom randomly with each pageview.