The Geek Clock($25) for really geek, where all the numerals have been replaced by the equivalent notation, if you can solve them all.

12 - the cubed root of 1728 
1 - Legendre’s constant is a mathematical constant occurring in a formula conjectured by Adrien-Marie Legendre to capture the asymptotic behavior of the prime-counting function. Its value is now known to be exactly 1. 
2 - A joke in the math world: An infinite number of mathematicians walk into a bar. The first one orders a beer. The second orders half a beer. The third, a quarter of a beer. The bartender says, “You’re all idiots,” and pours two beers. 
3 - A unicode character XML “numeric character reference.” 
4 - Modular arithmetic, also known as clock arithmetic, is a system of arithmetic for integers, where numbers “wrap around” after they reach a certain value. 
5 - The Golden Mean…reworked a little. 
6 - Three factorial (3*2*1=6) 
7 - Repeating decimal that rounds up to 7. 
8 - Graphical representation of binary code. 
9 - An example of a base-4 number, which uses the digits 0, 1, 2 and 3 to represent any real number. 
10 - A Binomial Coefficient 
11 An example of Hexadecimal encoding.

via (likecool)