Quadrophenia

To my Math class and other lovers of numbers, I give you the following.

You guys always had such an appreciation for all interesting number facts, such as the Fibonacci Sequence and its occurrences in nature, the Pythagorean theorem, and the Golden Ratio. You may recall the idea of imaginary numbers, which are, for instance, the square roots of negative numbers, and the double-answer to the square root of any number (such as the square root of 25 is both 5 and -5). Well, today I learned about two more.

The first is what is popularly called emirp numbers, more properly called reversible primes, which is a prime number whose digits can be reversed where the number is still prime. Example: 13 is an emirp number because if you take the digits and reverse them, you get 31, which is still a prime number. 13 was cited as the lowest emirp number, which I can only assume counts because not only is it a double-digit number, but also one where both digits are different. Otherwise, 11 would count.

Secondly, I learned that 13 is also the lowest happy number. This one gets a tad complicated. To be a happy number, which evidently has the same rules as emirp numbers in that it has to be a double-digit number, you must be able to take the squares of both numbers, add them together, add the resulting digits together, and get one for your answer. Example: Take 13. Take the squares of both numbers (1*1=1; 3*3=9), add them together (1+9=10), add those digits together (1+0=1). Because the answer is 1, 13 is therefore a happy number.

So take out those Mathcabulary Notebooks, guys, and add happy numbers and emirp numbers to them! You never know when these terms will come up in a trivia game of some kind.

Hope summer is going well, everyone.