Chinese numerology

In Chinese tradition, certain numbers are believed by some to be auspicious (吉利, ) or inauspicious (不吉, ) based on the Chinese word that the number sounds similar to. The numbers 3, 5, and 8 are generally considered to be auspicious, while 4 is considered inauspicious.
One.
The number 1 (一, ) is neither auspicious nor inauspicious. It is a number given to winners to indicate the first place. But it can also symbolize loneliness or being single. For example: November 11 is the Singles' Day in China, as the date has four ‘1’ which stand for singles.
Two.
The number 2 (二, cardinal, or 兩, used with units, ) is most often considered a good number in Chinese culture. In Cantonese, 2 (二 or 兩, ) is homophonous with the characters for "easy" (易, ) and "bright" (亮, ), respectively. There is a Chinese saying: "good things come in pairs". It is common to repeat characters in product brand names, such as the character 喜 (), can be repeated to form the character 囍 (). 
Three.
The number 3 (三, ) sounds like 生 (), which means "to live" or "life" so it's considered a good number. It's significant since it is one of three important stages in a person’s life (birth, marriage, and death).<br>On the other hand, number 3 (三,) sounds like 散 () which means "to split" or "to separate" or "to part ways" or "to break up with" so it is a bad number too.
Four.
The number 4 (四, ) is considered an unlucky number in Chinese because it is nearly homophonous to the word "death" (死 ). 
Thus, some buildings in East Asia omit floors and room numbers containing 4, similar to the Western practice of some buildings not having a 13th floor because 13 is considered unlucky. 
Where East Asian and Western cultures blend, such as in Hong Kong, it is possible in some buildings that the thirteenth floor along with all the floors with 4s to be omitted. Thus a building whose top floor is numbered 100 would in fact have just eighty one floors.
Five.
The number 5 (五, ) sounds like "me" in Mandarin (吾, ) and Cantonese (唔, ). 
Five is also associated with the five elements (Water, Fire, Earth, Wood, and Metal) in Chinese philosophy, and in turn was historically associated with the Emperor of China. For example, the Tiananmen gate, being the main thoroughfare to the Forbidden City, has five arches.
Six.
The number 6 (六, ) in Mandarin sounds like "slick" or "smooth" (溜, ). In Cantonese, 6 () sounds like "good fortune" or "happiness" (祿, 樂 ).
Therefore six is considered a good number for business.
Seven.
The number 7 (七, ) in Mandarin sounds like "even" in Mandarin (齊, ), so it is a good number for relationships. It also sounds like "arise" (起, ) and "life essence" (氣, ) in Mandarin.
Seven can also be considered an unlucky number since the 7th month (July) is a "ghost month". It also sounds like "to deceive" (欺, ) in Mandarin.
In Cantonese, 7 () sounds like 𨳍 (), which is a vulgar way of saying "penis".
Eight.
The number 8 (八, ) sounds like "發" ().
There is also a visual resemblance between 88 and 囍 (), a popular decorative design composed of two stylized characters 喜 ().
The number 8 is viewed as such an auspicious number that even being assigned a number with several eights is considered very lucky.
Nine.
The number 9 (九, ) was historically associated with the Emperor of China, and the number was frequently used in matters relating to the Emperor, before the establishment of the imperial examinations officials were organized in the nine-rank system, the nine bestowments were rewards the Emperor made for officials of extraordinary capacity and loyalty, while the nine familial exterminations was one of the harshest punishments the Emperor sentenced; the Emperor's robes often had nine dragons, and Chinese mythology held that the dragon has nine children.
Also, the number 9 sounds like "long lasting" (久, ), so it is often used in weddings.
Zero.
The number 0 (零, ) is the beginning of all things and is generally considered a good number, because it sounds like 'ling', which means 'good'.