Welcome to the sweet-16 birthday edition of the Playful Math Carnival. Originally called Math Teachers at Play, our first carnival was published in February 2009.
Each Playful Math Carnival offers a smorgasbord of delectable tidbits of mathy fun. It’s like a free online magazine devoted to learning, teaching, and playing around with math from preschool to high school.
There’s so much playful math to enjoy!
By tradition, we start the carnival with a math activity in honor of our 179th edition. But if you’d rather jump straight to our featured blog posts, click here to see the Table of Contents.
NOTE: Our wonderful volunteer hosts have kept the Playful Math Carnival going when so many other blog carnivals died off. If you’d like to sign up to host the carnival for a month, email Denise for information.
Try These Prime Puzzles
Did you know there are 179 even-numbered days this year?
- How many even-numbered days will there be in a leap year?
- But there are 365 days in a standard year and 366 in a leap year. Shouldn’t there be half that many even-numbered days?
179 is a prime number, and it’s also a knockout prime. You can knock out any of the digits, and what’s left is still prime: 17, 19, or 79.
- Can you find another knockout prime number?
179 is a twin prime. That means that one of its odd-numbered neighbors is also prime.
- Is the other twin 177 or 181? Can you tell without looking it up?
- Why are twin primes limited to the odd numbers? That doesn’t seem fair!
179 is also an emirp. That’s a special kind of prime that forms a different prime number when you write it backwards: 971 is also prime.
- How many emirps can you find?
“A palindrome is a word that when written in reverse results in the same word. for example, ‘racecar’ reversed is still ‘racecar’. Related to palindromes are semordnilaps. These are words that when written in reverse result in a distinct valid word. For example, ‘stressed’ written in reverse is ‘desserts’. Not all words are palindromes or semordnilaps.
“While certainly not all numbers are palindromes, all non-palindromic numbers when written in reverse will form semordnilaps.
“Narrowing to primes brings back the same trichotomy as with words: some numbers are emirps, some numbers are palindromic primes, but some are neither.”
—The On-Line Encyclopedia of Integer Sequences A006567
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Denise Gaskins' Let's Play Math 