Prime Time Fun revisited.

Another from the archives:


Is this funny to anyone who is not "mathematical"? Why is it funny to math-types? I worry that the later is wrapped up in some ego fed superiority concept.... I understand and "they" don't. For instance this is a tracer across the bottom of the cartoon site web page..

"Warning: this comic occasionally contains strong language (which may be unsuitable for children), unusual humor (which may be unsuitable for adults), and advanced mathematics (which may be unsuitable for liberal-arts majors)."

I hate that that might be true about me, but I still think it is funny.

Ok, as soon as I read it I started mentally checking for factors... eventually I decide that 1453 is prime. Now the math-teacher mind kicks in looking for variations of a theme. How common is it after 1 pm that the 12 hour clock is not prime and the 24 hour clock is, as in the example? The first example is at 1:19 / 13:19 (quick, factor that).



Is it more likely they are both prime? There are lots of examples of the latter right away, 101 and 1301 are both prime, as are 103 and 1303, 107 and 1307. Seems pretty common.



A reverse example occurs at 109/1309. The 12 hour clock is prime and the 24 hour clock is not, 1309=7 x 11 x 17; and again at 1:13.



Now admit it, you really can't get that much entertainment out of a typical comic.



Randall Munroe, who creates the XKCD comics says that he sometimes does this with mile markes on the highway. I guess I can admit that I find my self factoring the number on license plates and looking for interesting numbers. I still remember how pleased I was when I arrived on the base and received my PO box and the number was 1729; and only the math people know why.



Ok, while I'm admiting weird stuff... sometimes I just google a number to see where it shows up... 1729 was a good year for example, from my notes on Early American Math Textbooks, I find "In 1729 the first arithmetic published by a Native of Colonial America was published by Isaac Greenwood, a professor at Harvard. The title was Arithmetic, Vulgar (common) and decimal. Greenwood seemed to have a short and somewhat checkered life (1702-1745) He graduated from Harvard in 1722 and went on to become the Hollis professor of Mathematics, but was censured in 1737 for drunkedness and dismissed on August 30, 1738. He was replaced as Hollis professor, I believe, by John Winthrop of the Massachusetts Bay Winthrops." (by the way, 1722 is 42 x 41). 1729 is also the year that Danial Bernoulli invented a symbol for the inverse sine, he used AS. No one had ever made up an inverse sine notation before. Ok, just one more... "Benjamin Franklin advertised pencils for sale in his Pennsylvania Gazette in 1729"... and pencils brings us back to where we started, I used a yellow #2 to do all the factor doodles on the cartoon at the top... Life is a circle... or perhaps a Mobius Strip