The number 2 is a natural number that follows 1 and precedes 3. It is the smallest and the only even prime number. In mathematics, 2 is significant as the basis of duality and is used extensively in binary systems (base 2), which are fundamental in computing. It is also the first Ramanujan prime, the first superior highly composite number, and the first colossally abundant number
. As a word, "two" is commonly used as a determiner with plural countable nouns (e.g., "two days") or as a noun when referring to the number itself (e.g., "two plus two is four"). The English word "two" originates from Old English forms such as "twā," "tū," and "twēġen," with pronunciation evolving over time to /tuː/
. In geometry, two points define a unique line, and a digon is a polygon with two sides and two vertices. In set theory, a field must have at least two elements
. In science, 2 represents the number of electrons in the innermost electron shell of an atom
. Additionally, "2 On" is a popular song by Tinashe featuring SchoolBoy Q, released in 2014. The song is known for its catchy hook and themes of partying and getting "2 on," which refers to getting turned up or high
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