The number "14" is the atomic number for the element silicon, atomic weight or mass of nitrogen and the number of days in a fortnight. Valentine's Day occurs on Feb. 14. Fourteenth is the common designation for the actual 13th floor of some taller buildings due to superstitions around the number 13.
Atomic numbers are associated with the number of protons found in a particular element, which is why silicon's atomic number is 14; it has 14 protons. No other elements possess this atomic number because no other elements have the same amount of protons as silicon.
Valentine's Day is an international holiday occurring on Feb. 14. It is named after Saint Valentine who is recorded as dying in the year 269 CE on that day. The modern holiday is a day about love, affection and the symbolism of the heart. One custom prevalent in the United States is the exchange of valentines, tokens meant to signify affection for another person.
The practice of designating the 13th floor of a building as the "14th" is a result of superstition, and though the exact origin of that superstition is unknown, the phenomenon became common in New York City with the advent of modern skyscrapers.