What are some ideas for math topics to teach to gifted second and third grade math circle students? Let's assume the math circle meets for one hour every week.
One example activity is learning about various types of ciphers that can be used to send secret messages.
I know I can look at math circle archives online (and I have), but I think it'd be useful to compile a list of topics here. I'm curious to see what suggestions this community comes up with.
Edit: Archives for the Los Angeles Math Circle can be found here.
Also, a little background on math circles from Wikipedia:
Mathematical enrichment activities in the United States have been around for at least thirty years, in the form of residential summer programs, math contests, and local school-based programs. The concept of a math circle, on the other hand, with its emphasis on convening professional mathematicians and secondary school students on a regular basis to solve problems, has appeared only within the past twelve years. This form of mathematical outreach made its way to the U.S. most directly from Russia and Bulgaria, where it has been a fixture of their mathematical culture for decades. (The first ones appeared in Russia during the 1930s; they have existed in Bulgaria for a century.)