Today’s an international prime day

http://www.johndcook.com/blog/2013/11/29/todays-a-prime-day/

by ehamberg • 13 years ago

61 17 13 years ago

adorable• 13 years ago

So today is an international prime day because 291113 112913 20131129 are all primes

Today could also have been a "perfect prime day" if MM, DD, YY and YYYY had been prime (in addition to the above). But it's not the case...

11 -> is prime

29 -> is prime

13 -> is prime

2013 -> not prime (3 x 11 x 61)

Too bad! We will have to wait another 16 years before we have a perfect prime day...

ruttiger• 13 years ago

ya, but each of the factors of 2013 is prime, so that's gotta mean something, right?

gnur• 13 years ago

Isn't always possible to deconstruct the factors of a number in only primes?

PeekPoke• 13 years ago

Not prime here in the UK where we write our dates DDMMYYYY.

JonnieCache2• 13 years ago

In order of increasing duration, so you get to the most important information first. The correct order.

johndcook• 13 years ago

I like ISO format because then alphabetical order corresponds to chronological order.

Y-M-D and D-M-Y both have their advantages. Unfortunately my compatriots have standardized on M-D-Y, a convention that has no advantages that I can think of.

baby2• 13 years ago

so you get to the most important information first.

Very debatable. I've always found YYYYMMDD to be the most pertinent format as it gives you the "most important information first". As in, DD is unusable if you don't know the month, and the month is unusable if you don't know the year.

I like to picture a world where everyone use YYYYMMDD, the Metric system and English for technical terms (I'm from France and I hate when we invent new terms for technical terms).

pliny• 13 years ago

You don't, though.

You get the 2nd shortest duration first (tens of days) then the shortest (days) then the fourth shortest (tens of months) then the third shortest (months) etc

With the ISO standard every character symbolises a larger duration than the one that follows, so to get a strictly increasing order you have to reverse the string entirely - today would be 92-11-3102

Today’s an international prime day

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