Today's date, 11/11/11, is a once-in-a-century occurrence, adding to a November that has been a very fun month for recreational mathematicians.
Last week, a rare eight-digit palindrome date — 11/02/2011, which reads the same frontward and backward — was found to have other mathematical qualities that made it a once-in-10,000-years date. Aziz Inan, a professor of electrical engineering at the University of Portland in Oregon, crunched the numbers and found that when the date was expressed as a number, 11,022,011, it has very special properties.
"It is the product of 7 squared times 11 cubed times 13 squared. That is impressive because those are three consecutive prime numbers. No other palindrome date up to A.D. 10,000 is like that," Inan said. "Not only that, if you write it out as 72 x 113 x 132, you'll notice that even the superscript power numbers — 232 — are a palindrome."
A once-in-10,000-years date is hard to top, but 11/11/11 is no slouch. Some people believe that the date 11/11/11 is a mystical day of good luck, or that 11/11/11 is a good day to make money. Inan explained that when one looks closely at the date, it, too, has some interesting mathematical properties.
After today, 11/11/11 will next occur 100 years down the road, on Nov. 11, 2111. Interestingly, in 2111, 11/11/11 will be followed by an eight-digit palindrome day, 11/12/2111, which is quite exciting for palindrome fans like Inan.
If you consider today's date as a number — 111,111 — you can run some additional fun math tricks, Inan explained. 111,111 can be obtained from its largest prime number factor, 37, like so: First, subtract 37 from its reverse (73) and you get 36. (Inan added that 36 is equal to the square of the sum of the digits in 111,111.)
Then, split 36 into three consecutive numbers that add up to 36 (11, 12 and 13). Then, multiply 11, 13, 37 and the reverse of 12 (21). And what comes out? You guessed it: 111,111.
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