Fifteen is a triangular number, a hexagonal number, a pentatope number and the fourth Bell number.
Fifteen is the double factorial of five.
It is a composite number; its proper divisors being one, three and five.
With only two exceptions, all prime quadruplets enclose a multiple of 15, with 15 itself being enclosed by the quadruplet (11, 13, 17, 19).
Fifteen is also the number of supersingular primes.
In English, it is the smallest natural number with seven letters in its spelled name.
Fifteen is the number of letters in uncopyrightable, dermatoglyphics, misconjugatedly and hydropneumatics. These are the longest words without repeating a letter.
Fifteen is the number of days in each of the 24 cycles of the Chinese calendar.
In Tennis, 15 represents the first point gained in a game.
The number of players in Rugby Union is 15, with the full back wearing the number.
Fifteen is a number of deep esoteric significance to astrologers, numerologists and magicians across the world.
The Mystical Power of 15
Magicians consider it as alchemic vibration through which all magic is manifested.
Fifteen is considered “an extremely lucky number,” carrying the essence of enchantment. It is also associated with eloquence of speech and the creative aspects of music, art and drama.
It bestows upon the person or entity represented by it a dramatic temperament, strong personal magnetism and a curiously compelling charisma.
The vibration of Number 15 is believed to be especially fortunate for obtaining money, gifts, and favours from others, because of its powerful appeal to the altruistic nature of people.
People and entities born on the 15th day of any month carry with them high chances of success, reputation and enormous goodwill. Those with 15 as the compound number of their name would be blessed with the ability to bring great happiness to others and shine light into the darkness. They would also be involved in community and social service, dissemination of information and other creative areas.
The Number 15 reduces to six, which means service to others.
Source: Mathematics, Pure & Simple