The number one (1), also called "unity," is the first positive integer. It is an odd number. Although the number
1 used to be considered a prime number, it requires
special treatment in so many definitions and applications involving primes greater
than or equal to 2 that it is usually placed into a class of its own (Wells 1986,
p. 31). The number 1 is sometimes also called "unity,"
so the 
th roots of 1 are often called the 
th roots of
unity. Fractions having 1 as a numerator
are called unit fractions. If only one root, solution,
etc., exists to a given problem, the solution is called unique.
The generating function having all coefficients 1 is given by
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(1)
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The number one is also equivalent to the repeating decimal
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(2)
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(3)
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