$1000 High School Calculus Student Award (Math Chat)
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Frank Morgan, MAA Online  
Solution to the challenge: Justin Smith calls 5939 a "right" prime because it remains prime after dropping any number of digits from the right: 5939, 593, 59, and 5 are all prime. How many right primes are there less than 1000? Is there a largest right prime? Joseph DeVincentis, Jim Wiechmann, Chuck Diminnie, Eric Brahinsky, and Luke Gustafson find by exhaustive search that there are 27 right primes under 1000 and 83 right primes in all, the largest of which is 73,939,133. New challenge: On a beach in Oregon, at a certain moment, the very last bit of the Sun disappears below the horizon. The question is: Can I make that last bit of Sun reappear by jumping up quickly to my full height, or perhaps by very quickly running up the hill behind me, to increase the elevation of my point of view?  


Levels:  High School (912), College 
Languages:  English 
Resource Types:  Problems/Puzzles, Articles 
Math Topics:  Prime Numbers 
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