3

My favorite number is 3.  I have some personal facts about 3.  I was born on the third day of the month.  I am the third child in my family.  My first name starts with the letter C which is the third letter of the alphabet.  My last name starts with the letter K which takes three line segments to make.  I have three children.

Here are a some other facts about the number 3.

Three is the first odd prime number.
It is both the first Fermat prime (2²ⁿ + 1) and the first Mersenne prime (2ⁿ − 1), the only number that is both.

It is the first lucky prime.  A lucky number is a natural number in a set which is generated by a "sieve".  Begin with a list of integers starting with 1: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,  Every second number (all even numbers) is eliminated, leaving only the odd integers:  1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25,  The second term in this sequence is 3. Every third number which remains in the list is eliminated: 1, 3, 7, 9, 13, 15, 19, 21, 25,
The next surviving number is now 7, so every seventh number that remains is eliminated: 1, 3, 7, 9, 13, 15, 21, 25, When this procedure has been carried out completely, the survivors are the lucky numbers: 1, 3, 7, 9, 13, 15, 21, 25, 31, 33, 37, 43, 49, 51, 63, 67, 69, 73, 75, 79, 87, 93, 99, ... .
A lucky prime is a lucky number that is prime.  The first few are 3, 7, 13, 31, 37, 43, 67, 73, 79, 127, 151, 163, 193.

It is the only prime triangular number.


Three is the only prime which is one less than a perfect square. Any other number which is n² − 1 for some integer n is not prime, since it is (n − 1)(n + 1).

Three non-collinear points determine a plane and a circle.

Gauss proved that every integer is the sum of at most 3 triangular numbers.  An example would be 27 = 21 + 6.

Most elbows consist of three bones, the only joint in the human body where three articulations are surrounded by one capsule.

Earth is the third planet in its local Solar System.

Atoms consist of three constituents: protons, neutrons, and electrons.

We perceive our universe to have three spatial dimensions.

Many world religions contain triple deities or concepts of trinity, including: the Christian Holy Trinity, the Hindu Trimurti, the Hindu Tridevi, the Three Jewels of Buddhism, the Three Pure Ones of Taoism, and the Triple Goddess of Wicca.

 In Christianity, three people (including Jesus) were crucified at the Crucifixion.  Jesus laid dead in a tomb for three days before his resurrection.  The threefold office of Christ is a Christian doctrine that Christ performs the functions of prophet, priest, and king.

In Islam, during wudhu, the hands, arms, face and feet are each washed three times.  According to the prophet Muhammad, there are three holy cities of Islam (to which pilgrimage should be made): Mecca, Medina, and Jerusalem.