11-11-11 meaning: A special once-a-century repunit palindrome day

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Happy 11-11-11, everyone!

No matter how much thought you’ve given the numerical significance of Friday, Nov. 11, 2011 (11-11-11), we suggest that Aziz Inan, professor of electrical engineering at the University of Portland, has thought about it more than you have.

Inan has turned the consideration of palindrome dates into a sort of hobby, and earlier this month proved himself a master of detecting numerical patterns when he dazzled us with facts about Wednesday, Nov. 2, 2011 -- a very rare 8 digit palindrome date (11022011).


And now he’s back with some interesting revelations about 11-11-11.

PHOTOS: Eleven 11s: Just in time for 11-11-11

In an email missive, Inan explains that 11-11-11 is a once-in-a-century repunit palindrome day. If you’ve never heard of the word ‘repunit’ (our word-processing program had not), it means a number such as 11, 111, or 1111 that contains only the digit 1. ‘The term stands for repeated unit and was coined in 1966 by Albert H. Beiler,’ writes Inan.

Furthermore, he explains that 111111 equals the product of two palindrome numbers written as 111111=111 x 1001.

He points out that, this year, the month of November has been rich with palindrome days including 1-1-11 (another repunit day), 11-2-11, 11-3-11, 11-4-11, 11-5-11, 11-6-11, 11-7-11, 11-8-11, 11-9-11 and coming soon -- 11-22-11.

‘Among them, 112211 is interesting because it equals 101 x 11 x 101, a palindrome expression!’ he writes.

Although you may have already surmised that after this Friday, the next time 11-11-11 will occur is 100 years from now in 2111, you have perhaps not considered -- as Inan has -- that, ‘interestingly enough, in 2111, 11-11-11 and eight-digit palindrome day 11-12-2111 will be two concurrent palindrome days!’


And now for the final note: Inan reports that Nov. 11 is also his mother’s birthday. She will be turning 83. And 8 + 3 = 11.

Coincidence? Well ... probably.

Happy 11-11-11!


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