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Feb. 7! e (Euler's number) Day!

February 7 (2/7) is e (Euler's number) Day in America! In countries that do the date as date /

month, e Day was on January 27 (27/1).

What is e ?

"The number e is a mathematical constant that is the base of the natural logarithm: the unique number whose natural logarithm is equal to one. It is approximately equal to 2.71828,[1] and is the limit of (1 + 1/n)n as n approaches infinity, an expression that arises in the study of compound interest. It can also be calculated as the sum of the infinite series[2]

"Also known Euler’s number, after the Swiss mathematician Leonhard Euler, e is an irrational number that represents the idea that all continually growing systems are a scaled version of a common rate. It is mostly used in logarithms, exponential growth, and complex numbers. It is one of the most important numbers in mathematics, including 0, 1 and pi (π)."


"So what is e good for? See Exponential and Logarithmic Functions.

It is used extensively in logarithms (which was the only way to do difficult calculations for hundreds of years before calculators came along), exponential growth (of populations, money or drug concentrations over time) and complex numbers (which were used to design the computer or mobile device you are reading this on)."


Plus Magazine: Living Mathematics website (link below) has a lot of good articles on e and its relevance in everyday life: compound interest (money!), in nature and in science (e.g. radioactive decay, etc.)



For e day,

I made 2 cookies. I used the sugar cookie and non-Royal Icing icing for both cookies (link).


One I made to resemble a chalkboard with e to 18 decimal points. To get the white icing to show up, I had to let the black background set completely and then do the white icing later.

The other I made to resemble a TI-83 calculator, which I used growing up when I was first learning about e. It's a little rough looking. Haha. :) For the calculator, I made the buttons out of marshmallow fondant (link). I could have made the buttons more regularly shaped, but I got tired. Haha. :)


Happy e day! Give it a try! We are good at this!

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