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.
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.