JOHN YDSTIE, host: People have favorites, that's how we're built. We have favorite foods, favorite movie stars, favorite colors. But there's a category of favorocity you may not have considered - until now. Here's our science correspondent Robert Krulwich.
ROBERT KRULWICH: Alex Bellos writes books about mathematics.
ALEX BELLOS: Yes.
KRULWICH: And whenever he gives a talk.
BELLOS: Usually, at the question time at the end, someone would put up their hand and say, what's your favorite number?
KRULWICH: Favorite number.
BELLOS: And this would infuriate me.
KRULWICH: Because it's such a dumb question, he thought.
BELLOS: What does that mean to have a favorite number? How can I choose one over the other? Maybe I'm just too sort of rational, I think...
KRULWICH: But just to be fair, Alex decided, well, you know, why don't I just look into this? So, for fun a few months ago, he set up a website which he calls WhatsYourFavoriteNumber.net. And he simply asks people do you have a favorite number, and if you do, could you tell me what it is and tell me why? So far, he's gotten 22,000 responses.
BELLOS: Amazing. I'm overwhelmed with data.
KRULWICH: And people are writing him from all over the world.
BELLOS: They're incredibly passionate about it. And people are, you know, sending me poems about numbers and saying things like, you know, I really love four but I cannot abide three and all this stuff gushes out. It's as if people have never been allowed to talk about this before. It's like this love of numbers was the love without speak his name. Who would have thunk it really?
KRULWICH: Looking through the responses thus far, he says:
BELLOS: The most common reason for having a favorite number is it's the day I was born.
BELLOS: But then it tends to only be if you were born on the third, the fifth, the ninth, the eleventh, the thirteenth.
KRULWICH: So, if your birthday is, like, the 10th or the 30th, you don't choose it as a favorite?
BELLOS: It just doesn't happen.
KRULWICH: Really. 'Cause there seems to be kind of a weird preference here for prime numbers.
BELLOS: But why is it that primes are seen as more favorite?
KRULWICH: Well, the thing about primes is they're indivisible. So, because you can't divide them...
BELLOS: There makes something kind of strong and almost trustworthy.
KRULWICH: Right, exactly.
BELLOS: And there's one very funny submission came in. They said I like 73 because it's the Chuck Norris of numbers. And so it's the Chuck Norris of numbers because it's prime - 73 - so really tough. But if you do the mirror prime, turn it around - 37 - that's also prime. So, it's kind of like 73 is the number that's got it's back covered.
KRULWICH: At this point - and he's keeping this site all summer long - right now, across gender, across continents, across cultures, a few numbers have taken an early lead.
BELLOS: It's not giving anything away to say that of, you know, the leading contender is the number seven.
KRULWICH: Which is a lucky number in a lot of cultures. But then there's also:
BELLOS: Three, 11 and 13.
KRULWICH: And they're all prime numbers, or maybe they're all low numbers.
BELLOS: No, because one and 10, for example, almost never appear.
KRULWICH: Alex says people seem to have two kinds of favorites. Some like a number because of the way it divides or multiplies or its roots.
BELLOS: More mathy(ph) type thing.
KRULWICH: And others are more lovey-dovey and sort of Fantasia-ish, you know. So, for the number eight, for example:
BELLOS: People say, oh, I love its shape. It's sort of soft and round and comforting. You also get, you know, silly things, like, one number which is quite popular among kind of student-age people, I guess, is 5,318,008.
BELLOS: Because if you put that in a computer, you get boobies. But what's also interesting as today...
KRULWICH: As in breasts? You mean boobies as in breasts?
BELLOS: As in female breasts, yeah.
KRULWICH: Meaning if you type the digits 5-3-1-8-0-0-8 into a calculator, say, and then you turn the calculator upside down and you look at the numbers, they will look roughly like the English spelling B-O-O-B, you know, for boobies.
BELLOS: But what's interesting is today I got a number from Finland, and he liked 715,517, because that spells tiffit(ph), which in Finnish is boobies.
(SOUNDBITE OF LAUGHTER)
BELLOS: This is a kind of cross-cultural connection between female breasts and numbers that I never knew existed.
KRULWICH: Alex will tally all the answers he's getting to see if there are age differences or gender differences or class differences for favorite numbers. And if things work out, he says:
BELLOS: Well, ideally, it would be great to say with some kind of authority this number is officially the world's favorite number. I'm not sure I'm going to get that because...
KRULWICH: I don't think you will.
BELLOS: ...you know, half of China, I get no answer.
KRULWICH: But just this month, he got a surge of more favorite numbers from China. So, if you want to help him out here, again, is the site. It's www.favoritenumber.net. Robert Krulwich, NPR News.
(SOUNDBITE OF SONG, "THREE IS THE MAGIC NUMBER")
SCHOOLHOUSE ROCK: (Singing) Three, six, nine, 12, 15, 18, 21, 24, 27, 30. Three, six, nine, 12, 18, 21, 24, 27, 30...
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