Why odd numbers are dodgy, evens are good, and 7 is everyone's favourite

The Japanese love odd numbers. When you give gifts you must always give three, five or seven items. Photograph: D. Hurst / Alamy/Alamy

Think of the number 7. Do you like it? Do you love it? Do you remain unmoved?

You may think these are frivolous questions, but when I launched an online survey asking people to submit their favourite numbers – and explain the reasons why – almost 4,000 people declared a devotion to 7.

"[It] cheers me up and gives me a feeling of comfort," said a female participant, aged 48, from Norway.

"[It] has great symbolic value as an expression of Muslim belief and the miracles of God," wrote a 25-year-old man in Lebanon.

"[It] is the best. Like a nice and clever woman," added a Hungarian man, aged 20.

Seven polled the highest in my global survey, making it – in my opinion – the world's favourite number, a result I revealed last week on myGuardian blog, and which was written up in news outlets across the world.

The survey, which attracted 44,000 participants, was self-selecting and therefore did not conform to the rigorous standards of a laboratory experiment. (Although I would wager than any professional poll would find the same results.) Yet academic studies that have investigated our emotional responses to numbers have found that they follow clear patterns.

Marisca Milikowski of the University of Amsterdam set up an experiment in which participants were shown all the numbers between 1 and 100 and asked to rank each number on a scale between good and bad, and between excitable and calm. Her results showed quite clearly that, in general, even numbers are seen as good, and odd numbers bad. Numbers ending 1, 2 or 3 are generally more excitable than the others, and even numbers are the most calm.

Dan King of the National University of Singapore and Chris Janiszewski of the University of Florida asked participants whether they liked, disliked or felt neutral about every number between 1 and 100, as the numbers appeared in random order on a screen. Data from this experiment showed that even numbers and ones ending in 5 are much better liked than the other odd numbers.

In other words, when asked to project non-mathematical meanings on to numbers, or to react emotionally to them, our responses are remarkably coherent. And these responses reflect numerical properties, most clearly size and divisibility by either 2 or 5.

It is interesting that our favourite number is 7, an odd number, when even numbers are more liked and seen as calmer and better than odd numbers. In fact, in my survey, favourite numbers are much more likely to be odd than even, with a ratio of 60/40. Counter-intuitively, our favourite numbers are generally not the ones we like best or rate as good. Like is very different from love.

We can explain the popularity of 7 as a favourite number by looking at a classic psychology experiment. When asked to think of a random number between 1 and 10, most people will think of 7. Our response is determined by arithmetic. The numbers 1 and 10 don't feel random enough, neither does 2, nor the other even numbers, nor 5, which is right in the middle … So we quickly eliminate all the numbers, leaving us with 7, since 7 is the only number that cannot be divided or multiplied within the first 10. Seven "feels" more random. It feels different from the others, more special, because – arithmetically speaking – it is.

Terence Hines of Pace University in the US conducted another experiment that helps explain why we view odd and even numbers differently. He displayed pairs of digits on a screen. These would be both odd, like 1 and 3; both even, like 6 and 8; or one of each, like 1 and 6. Participants were asked to press a button only when either both digits were even or both digits were odd. On average it took respondents 20% longer to press the button when both digits were odd. He calls it the "odd effect" – it takes our brains longer to process odd numbers. They are literally more thought-provoking.

When people explained their choices in my favourite number survey, their reasons were varied and surprisingly tender, such as 2 because the respondent has 2 piercings, 6 because the sixth track on the respondent's favourite albums is always the best, 17 for the number of minutes the respondent takes to cook rice, 24 because the respondent sleeps with her left leg kicked out like a 4 and her boyfriend sleeps like a 2 on his side, and 1,000,000,007 because it is the highest prime number he can remember.

"Having a favourite number means that you get a little buzz every time you happen to be sitting in seat 53 on a train, or notice that the time is 9.53," said one submission. "I can't think of a reason not to have a favourite number."

We learn at school that numbers are tools for counting, but our relationship with numbers is quite clearly a deep and complex one, dependent on many cultural and psychological factors.

In the far east, superstitions about numbers are more noticeable than in the west. For example, 4 is unlucky for speakers of Mandarin, Cantonese, Japanese and Korean because the word for "4" sounds the same as that for death. Brands avoid product lines with a 4 in them, hotels don't have fourth floors and aircraft don't have fourth rows. (This is more disruptive than western fear of 13, primarily since, being smaller, 4 occurs more often than 13).

Eight is a lucky number in east Asia, however, because it sounds like the word for prosperity. A study of newspaper adverts in China, Taiwan and Hong Kong showed that 8 is by far the most popular non-zero digit in a price (for example in ¥6,800, ¥280). If you put an 8 in your price you make the product seem much more alluring.

These superstitions are not lightly held. Indeed, the association of 4 with death has become a self-fulfilling prophecy. US health records show that, for Chinese and Japanese Americans, the chance of suffering a fatal heart attack is 7% higher on the 4th of the month than would be expected.

East Asians hold deep superstitions about numbers, yet outperform western nations in the international league tables of mathematical performance, which suggests that strong mystical beliefs about numbers are not an impediment to learning arithmetic skills.

In fact, I would argue that having any sort of belief about numbers encourages a playfulness and an intimacy with them, which ultimately makes you less scared of mathematics and better at sums. It pays to have a favourite number.

Alex Bellos's latest book is Alex Through The Looking-Glass, Bloomsbury, £18.99. To buy a copy for £15.19 with free UK p&p call 0330 333 6846 or visit guardianbookshop.co.uk. He tweets at@alexbellos

• This article was amended on Sunday 13 April 2014. We said originally that participants were asked to press a button only when both digits were odd. This should have read participants were asked to press a button only when either both digits were even or both digits were odd. This has been corrected.

THE ODD COUNTRY

■ The Japanese love odd numbers. When you give gifts, you must always give three five, or seven items.

■ When giving cash at a wedding, the preferred amounts are ¥30,000, ¥50,000 and ¥100,000. If, however, you don't want to pay more than ¥20,000, you have to "odd things out" by dividing that sum into one ¥10,000 and two ¥5,000 bills.

■ The obsession with odd numbers is so great in Japan, according to Professor Yutaka Nishiyama of the Osaka University of Economics, that when in 2000 the government released a ¥2,000 note, no one ever used it.

■ Odd numbers underlie more than just Japanese ideas about money. Inikebana, the traditional form of flower arranging, only odd numbers of stems are used, following the Buddhist belief that asymmetry reflects nature.

■ A restaurant serving kaiseki, a form of multi-course haute cuisine, serves always an odd number of dishes.

■ The annual children's celebration is called the Seven Five Three festival, in which only children who are aged seven, five and three can take part.