Never travel on the 17th day of the month, don't live on the fourth floor of a building and always look for the number eight. These are just a few of the popular beliefs about numbers from different cultures across the world.
Numbers are especially important in parts of South East Asia which share similarities in language.
May Hu, of SBS Radio's Mandarin program, says it's partly due to the sounds of the words for certain numbers.
"Because number 8 in Chinese - bÄ, is similar to the word of fÄ - bÄ and fÄ - that means to be rich. And they also like number six. Number six means like in English 'sailing' or going through without any trouble. If you're going out for long travel or doing some business they would like to have the number six. And they dislike the number four, because four in Chinese 'sì' is similar to the word for death, in Chinese it's 'sei'.
Tetraphobia - which literally means the fear of four - is used to describe the practice of avoiding instances with the number four.
Phone companies in China have reported receiving a high number of requests for phone numbers containing eights.
And some high-rise buildings in China have no fourth floor, instead skipping straight from the third floor to the fifth.
"And the interesting thing is (with) the real estate agents in China.. level four, nobody buys them. And they will find in some occasions, level four will be very cheap".
May Hu says such beliefs about numbers can have very real implications on people's lives, and the choices they make.
"When you get married you have to match the wife and husband so they have both of the 8 numbers to match together. If they don't match, then the Feng Shui Master will say, 'You will quarrel and your family won't be happy and you'll get divorced,' or things like that."
A belief in lucky numbers crops up in other cultures.
Forty holds special significance for many Lebanese Christians, possibly from the Biblical reference to 40 days and 40 nights.
Some Muslims in Myanmar and the Indian subcontinent place special importance on the number 786, because the sum of the letters in Arabic can be translated to mean, "begin with the name of God who is very merciful".
In Bulgaria, it's three, four and seven: three symbolising the earth, sky and underground; four for the points of the compass; adding up to a total of seven.
Sylvia Pianelle of SBS Radio's Italian program says 17, and particular Friday the 17th, is considered unlucky by many in Italy, while 13 is a lucky number.
"Some people don't like to travel on Friday the 17th, so when if they book a holiday or something they like to check. Because they just consider they might end up having a late trip or just little daily annoying things".
Sylvia Pianelle says the idea that 17 is unlucky has persisted, even though most people wouldn't know where it originally came from.
New York-based author Matthew Hutson says one explanation for this is that the Roman numeral for 17, XVII, is an anagram for a Latin word which means 'I have lived' or 'My life is over' - the same words uttered by the ancient Roman ruler Marcus Cicero at executions.
"A lot of these numbers they have some origin in mythology or history, and they gain these positive or negative associations. And then maybe we forget about the original meaning, or the original association but we still think of the number as positive or negative."
Matthew Hutson has written a book about superstitions called "The 7 Laws of Magical Thinking".
He says beliefs about numbers can be self-fulfilling: for instance, if people believe a day to be unlucky, they may interpret or notice events on that day as being bad.
And he says superstition, what he calls 'magical thinking', can be destructive if people rely on it too heavily, or become obsessive.
The flip-side of this, according to Matthew Hutson, is that people can take advantage of their beliefs in luck in order to achieve positive outcomes.
"There are experiments showing belief in luck can enhance confidence and can enhance performance. There's one study in which subjects were handed a golf ball and half the subjects were told that the golf ball was a lucky golf ball. And these subjects actually made about 35 per cent more successful puts than the other subjects".
Matthew Hutson says although it won't help to predict lottery numbers, a belief in lucky numbers can actually make people more lucky.
"If there's no other way to get control, then just getting the sense of control through superstition, can relax you and increase your confidence. Belief in magic can also bring a sense of meaning in the world, if you feel that things are meant to happen, for instance, or that there's some sort of deeper structure in the universe or the events in your daily life. It's sort of like Dumbo's magic feather, you know, he had this feather that he thought made him fly, but really it was just him. But just believing he could fly helped him fly.'
