6 - 六liù
The number 6 is generally considered to be lucky in China because 六 sounds like 流 (liú), which means "flow" in Chinese. The number 6 is symbolic for being well-off. Multiple numbers of sixes are considered extremely lucky. Unlike in western culture triple six is seen as a very evil and ominous number or the sign of the devil but in Chinese culture "666" is held in high regards and considered a very lucky number. This cultural difference will probably cause a western traveler in China to gasp at the sight of "666" numbers blasted on flyers and t-shirts because many businesses display the number 6 as a sign of good fortune. There's also a popular Chinese idiom, 六六大顺 (liù liù dà shùn), which means that things will go smoothly.
7 - 七qī
7 has both positive and negative connotations in Chinese culture. For the positive side, 七 sounds like both 起 (qǐ), which means "start" or "rise", and also 气 (qì), which means "vital energy". Seven is also seen as a lucky number for relationships. The Qixi Festival (七夕節), also known as the Chinese Valentine's Day, falls on the 7th day of the 7th month in the lunar calendar. For the negative side, the 7th month is also known as the "ghost month" in China, where ghosts and spirits are believed to rise from hell to visit earth. While ghosts may be seen as omens, the ghost festival in the 7th month is widely celebrated. 7 may also be considered unlucky because 七 sounds like 欺 , meaning "cheat".