4 - 四sì
4 is well known to be an unlucky number because 四 sounds similar to 死 (sǐ), which means "death" in Chinese. 4 has an ominous point of view similar to the number "13" in the western world. Because of this, 4 is avoided in all aspects. The number 4 is not to be uttered too often and not to be put on display because it's perceived to bring bad karma, misfortune and an overall death vibe. As a result of this belief the number 4 is often omitted from building addresses, ID numbers, phone numbers, license plates, clothing, company names and logos. When constructing buildings the fourth floor is often left out, blocked out or skipped over. In buildings, the floors might go from the third floor directly to fifth floor, or the fourth floor is replaced with 5A. Giving anything to someone that has the number four is offensive to say the least.
5 - 五wǔ
The number 5 is considered a neutral number in China but still considered more lucky than unlucky. The number five is relevant as a lucky number because there are five blessings in China, which is wealth, happiness, longevity, luck and prosperity. 5 is lucky in that regard. 5 is thought to be a neutral number because in Chinese the number five sounds similar to无 (wú), which means "nothing" "without" which can mean neither good or bad.