In case you forget…

2011 is a prime number year, which makes this a prime number year. The next prime number year will be 2017. That means we have just two prime number dates — when day, month, and year are all prime numbers — left this year: 11/23/2011 and 11/29/2011. Then we will have to wait until February 2, 2017, for another prime number date.

I figured I had better tell you in case you wanted to do something special on Wednesday, or a week from Tuesday.

Prime number days and consecutive odds days

Today’s date is made up entirely of prime numbers: 7, 5, and 2011. I’m sure you already noticed that, because you’re already aware that 2011 is a prime number, and so you’re watching for the fifty-two dates this year made up entirely of prime numbers. Which means that you have also noticed that there are three prime number Sundays this month, which is the greatest number of prime number Sundays you can have in any month.

However, you may not have thought about the fact that Saturday’s date is made up of consecutive odd numbers (if, that is, you define the number of the present year to be 11, as it is often written, rather than 2011). Ron Gordon of Redwood City has thought about it, and has received national press in his efforts to promote what he calls Odd Day. I’d have to say that a more precise name would be Consecutive Odds Days, but I recognize that “Odd Day” is a catchier name.

Using Gordon’s definition, there are six Odd Days per century. For purists who believe that a number is a number, dammit, and you can’t just arbitrarily chop off the digits to the left of the tens place, there were only six true Odd Days ever using our present system of numbering years, and those happened even before our present system was in place. While this notion might disturb you, it is probably more satisfying to the pure mathematician, for the pure mathematician prefers things that don’t actually exist.


I got on a BART train today at about two in the afternoon. An ad next to the door of the train proclaimed:

Judgment Day
May 12, 2011

At six o’clock, the predicted time when Judgment Day was going to come (725,000 days after Jesus was executed, or something like that), I was sitting eating dinner with some friends. “We’re still here,” someone said.

I just went to check the Web site of Family Radio — that’s the Web site controlled by Harold Camping, the guy who’s been predicting the end of the world. Their Web site is still up and running, and it still says:

Judgment Day
May 21, 2011
00 days left

And their radio station is still broadcasting (they stream it live on the Web site if you want to check it out) — and the announcer just said that he’ll back back again tomorrow.

I guess that means the Rapture is off. So what happened? Was it supposed to be 7,250,000 days, not 725,000 days? Does God count in hexadecimal? Or maybe God prefers prime numbers (this is a prime number year after all) so it’s going to be the next largest prime, 725,009?

I’m sure they’ll come up with some reason or another why the Rapture didn’t come today. And I would love to hear your speculations on where they did their math wrong.

Happy prime new year

This is going to be a prime year, and by that I don’t mean it’s going to be first-rate (though I don’t rule that out) — rather, 2011 is a prime number.

Since 2011 is a prime number, that means we can look forward to having several dates that consist solely of prime numbers. The first one will be 2/2/2011, and the last 11/29/2011. I leave it as an exercise to the student to determine how many of these dates will occur all year (translation: I’m too lazy to figure it out myself, and I hope someone will post a comment with the answer). *

The last prime number year was 2003, and the next one will be 2017. While searching for lists of primes on the Web, I discovered that 2011 and 2017 are so-called “sexy primes”; that is, they differ by six (“sexy” from the Latin “sex” for six); if they differed by four, they would be cousin primes, and if by two, twin primes. Thus 2011 is a sexy prime number year.

I suspect I am fascinated by prime number years because I was born in the middle of the largest gap in prime number years in the twentieth century (1951 to 1973). I had to wait more than a decade to live in a prime number year; I had a deprived childhood.


* Here’s the list of primes 31 and under: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31. Don’t say I didn’t help you out. Oh, all right, the answer is 52.