Palindrome day: Patterns of the calendar make for numerical fun

By Tom Vogt, Columbian science, military & history reporter

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Happy Jan. 2, 2010 … and not just because we’re at the second day in what some folks call a new decade.

For just the second time in more than six centuries, the date can be read as a mirror image.

Did you know?

January is an appropriate month for date-based palindromes. It’s named for Janus, a Roman god depicted with two faces looking in opposite directions.

In month-day-year format (MM-DD-YYYY), it can be written as 01-02-2010, which is the numerical version of a palindrome. That’s a word (rotator) or phrase (Madam, I’m Adam) that reads the same backward and forward.

The last time this happened was Oct. 2, 2001 — or 10-02-2001 — said Aziz Inan, a professor of electrical engineering at the University of Portland.

And before that? You have to go back a bit.

“The amazing thing is, the one before that was Aug. 31, 1380 or 08-31-1380,” said Inan, a math puzzle enthusiast. “That was 620 years ago.”

Our next one — the third of 12 palindrome dates in the 21st century — will pop up Nov. 2, 2011 or 11-02-2011.

21st-century palindrome dates

10-02-2001

01-02-2010

11-02-2011

02-02-2020

12-02-2021

03-02-2030

04-02-2040

05-02-2050

06-02-2060

07-02-2070

08-02-2080

09-02-2090

“Palindrome dates are notably rare. They only occur in the first few centuries of a millennium,” said Inan, who was featured last week on the puzzle corner of the New York Times’ Web site.

The 36th and last palindrome date of this millennium will occur on Sept. 22, 2290. The next one after that will be Oct. 3, 3001.

Inan said he came to palindromes through an earlier fascination with numbers.

“My hobby is playing with ages and numbers and historical dates. That’s how I stumbled on this,” he said.

He points to the number 48 as an example: “Take 4 squared and 8 squared, subtract it, and you get the original number back,” he said.

That’s 64 – 16 = 48, and “It’s the only two-digit number with that property,” Inan said.

A couple of years ago, he bought a used volume at Powell’s Books that listed things like squares and cubes of all numbers from 1 to 10,000.

At first, he was interested in perfect square years (like 1849 and 1936) and cubic years (like 1331 and 1728), he said.

Then he came across the perfect square number 4012009 (it’s 2003 x 2003).

“It occurred to me that it’s the full date for April Fool’s Day for 2009.”

He started playing with other “MM-DD-YYYY” date combinations. And that helped guide him to calendar palindromes.

Other parts of the world abbreviate their dates differently, by the way, leading with the day in a “DD-MM-YYYY” format.

Inan has worked those combinations, too.

“We have 12 palindrome dates this century; the rest of the world has 29,” he said. “Our 12 all will occur on the second day of the month. Theirs all occur in February.”

A playful approach to numbers has more than just recreational value, Inan says. It can be a valuable educational tool. It can show students another side of a subject that often is intimidating, yet is a backbone of civilization.

After he discussed palindrome numbers with his students, many of them started playing with elements of their own birthdates.

The U of P prof doesn’t limit this sort of thing to numbers. Take his name …

Print AZIZ in all capital letters; turn each Z on its side, and then swap the vowels. The result? His last name, INAN.