In two dimensions, a digon is a polygon with two sides (or edges) and two vertices. On a circle, it is a tessellation with two antipodal points and 180° arc edges. The simplest tessellation in two-dimensional space, though an improper tessellation, is that of two 
  
    
      
        ∞
      
    
    {\displaystyle \infty }
  -sided apeirogons joined along all their edges, coincident about a line   that divides the plane in two. This order-2 apeirogonal tiling is the arithmetic limit of the family of dihedra {p, 2}. For any polyhedron homeomorphic to a sphere, the Euler characteristic is χ = V − E + F = 2, where V is the number of vertices, E is the number of edges, and F is the number of faces. The long diagonal of a regular hexagon is of length two when its sides are of unit length. Whereas a square of unit side length has a diagonal equal to the square root of two, and a cube of unit side length has a space diagonal equal to the square root of three, a space diagonal inside a tesseract measures two when its side lengths are of length one. There are two known sublime numbers, which are numbers with a perfect number of factors, whose sum itself yields a perfect number.
12 is one of the two sublime numbers, with the other being 76 digits long. List of basic calculations
In science
The number of polynucleotide strands in a DNA double helix. The first magic number. The atomic number of helium. The ASCII code of "Start of Text". 2 Pallas, a large asteroid in the main belt and the second asteroid ever to be discovered. The Roman numeral II (usually) stands for the second-discovered satellite of a planet or minor planet (e.g. Pluto II or (87) Sylvia II Remus). A binary star is a stellar system consisting of two stars orbiting around their center of mass. The number of brain and cerebellar hemispheres. In sports
The number of points scored on a safety in American football
A field goal inside the three-point line is worth two points in basketball. The two in basketball is called the Shooting Guard
2 represents the catcher position in baseball. Other
In pre-1972 Indonesian and Malay orthography, 2 was shorthand for the reduplication that forms plurals: orang (person), orang-orang or orang2 (people). In Astrology, Taurus is the second sign of the Zodiac. For Pythagorean numerology (a pseudoscience) the number 2 represents duality, the positive and negative poles that come into balance and seek harmony. See also
List of highways numbered 2
Binary number

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External links

Prime curiosities: 2