1, pronounced y and, is one of the natural numbers. 1 is an Arabic numeral, the smallest positive integer, and an integer between and 2, the smallest positive odd number. 1 is a rational number, a single digit and a singular number, and 1 is a Heegner number.
1 is neither a prime number nor a composite number. The first thing expressed through the unit. The whole composed of one or several things can be regarded as the unit "1".
1 is a simple Arabic numeral. 1 to the nth power (n∈R) is equal to 1.
Extended information
1. Mathematics field
1 is Arabic numerals.
2. Computer science
is often used to express the "true" value of Boolean values, and 1 is also the largest singular value in binary, similar to 9 in decimal.
3. Geometrical optics
The refractive index of vacuum is 1
4. Astronomy:
The average distance between the sun and the earth is 1 astronomical unit.