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Maths geeks around the world are celebrating a day so rare that - unless they're very, very young - it's certain to happen only once in their lifetimes.

This is, of course, palindrome day, when the date - in this case 02/02/2020 - reads the same way back to front.

But while palindrome days come and go - 20/02/2002 is another example - this one is special.

Unlike the date in 2002, this one reads the same in the US, where dates are written as month-day-year instead of day-month-year as in much of the rest of the world.

It also works for China and a handful of other countries which put the year first.

The last time a palindrome like this happened was 11 November 1111. (Which is really beside the point, because no-one was using our current dating systems in those days anyway.)

In that year:

• Crusaders led by Baldwin I of Jerusalem were fighting the Turks in what is now northern Syria
• Henry I, fourth son of William the Conqueror, was king of England
• Afonso I, founder of the kingdom of Portugal, was born

We don't have to wait quite so long for the next international palindrome day, though - it's 12 December 2121. Who knows? Some of us may even live to see it.

Those who are super-engaged with dates and numbers will have pointed out another anomaly.

Sunday 2 February is number 33 in days of the year - 33 being another palindrome. And as this is a leap year, it's also 333 days from the end of the year - a third palindrome.

Meanwhile, many social media users have been pointing out that this palindrome day coincides with another major event in the North American calendar.

As the dawn came up over the US state of Pennsylvania, the world's most famous groundhog, Punxsutawney Phil, predicted an early spring.

International palindrome dates:

• 01/01/1010
• 11/11/1111
• 02/02/2020
• 12/12/2121
• 03/03/3030
• 04/04/4040
• 05/05/5050