# Tag Archives: prime

## Why Two is My Favorite Number

Many math geeks will pick a favorite number of theirs because of a certain property of said number. Some people choose e, the base of the natural logarithm, some choose π, the ratio between a circles circumference and its diameter, some clever few choose i, the square root of -1, and some people choose a natural number, that is, a positive integer, that has some significance to them, be it 17, 300, 132, or any other number. I choose two (2) as my favorite number and here’s why:

• 2 defines what numbers are even, and what numbers are odd.
• 2 is the first prime number, the smallest prime number and only even prime number. 2 and 3 are the only two consecutive primes.
• The decimal expansion of any simple fraction where the denominator is 2 will always terminate in a 5 or a 0, depending on whether the numerator is even or odd.
• 2 is the base of binary, the number system with the smallest base in which numbers can be written (relatively) easily.
• 2+2=2×2=2^2=2↑↑2=…=4. x↑↑y is called tetration, I’ll go over it later.
• 2 is its own factorial.
• 2 is part of a bunch of other special prime categories, like Fibonacci primes, Lucas primes, factorial primes.
• 2 is a highly composite number, meaning it has more positive whole number factors than any number less than it.
• There are two characters for two in Chinese, 二 and 两.
• 2 is the atomic number of helium, the first noble gas.
• Mersenne primes are found using powers of two.
• The square root of 2 (about 1.414) was the first irrational number to be discovered.
• 2 is the fewest number of dimensions needed for polygons to exist in geometry.
• And finally, a superficial one, my birthday is in February, the second month in the Gregorian calendar.