For example, three and seven together in Cantonese emphasizes that you not only are able to grow, but you can also grow out of any situation you might be trying to have. It is for this reason it is auspicious. If it was combined with the numbers 4 and 5, i.e. 457, this would be extremely inauspicious as it would translate literally to “Death does not allow you to leave” or interpreted “Even in death you cannot escape.” 

The number 7 (七qī) symbolizes “togetherness” in Chinese. It is a lucky number for relationships. It is also recognized as the luckiest number in the West, and is one of the rare numbers that is great in both Chinese and many Western cultures. It is a lucky number in Chinese culture, because it sounds alike to the Chinese word 起(qǐ) in Mandarin meaning arise, and also 气(qì) meaning life essence. In Cantonese it sounds like the verb “to leave” which adds emphasis.