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The requirement that the factors be prime is necessary: factorizations containing composite numbers may not be unique (for example, = =). This theorem is one of the main reasons why 1 is not considered a prime number : if 1 were prime, then factorization into primes would not be unique; for example, 2 = 2 ⋅ 1 = 2 ⋅ 1 ⋅ 1 ...
More precisely, it can be shown that if n has 1 or 2 odd prime factors (for example, n = 150) then the n th cyclotomic polynomial only has coefficients 0, 1 or −1. Thus the first conceivable n for which there could be a coefficient besides 0, 1, or −1 is a product of the three smallest odd primes, and that is 3 ⋅ 5 ⋅ 7 = 105 .
Continuing this process until every factor is prime is called prime factorization; the result is always unique up to the order of the factors by the prime factorization theorem. To factorize a small integer n using mental or pen-and-paper arithmetic, the simplest method is trial division : checking if the number is divisible by prime numbers 2 ...
Every real number x has exactly one real cube root that is denoted and called the real cube root of x or simply the cube root of x in contexts where complex numbers are not considered. For example, the real cube roots of 8 and −8 are respectively 2 and −2.
Because the prime factorization of a highly composite number uses all of the first k primes, every highly composite number must be a practical number. [8] Due to their ease of use in calculations involving fractions , many of these numbers are used in traditional systems of measurement and engineering designs.
lcm(m, n) (least common multiple of m and n) is the product of all prime factors of m or n (with the largest multiplicity for m or n). gcd(m, n) × lcm(m, n) = m × n. Finding the prime factors is often harder than computing gcd and lcm using other algorithms which do not require known prime factorization.
Small Eisenstein primes. Those on the green axes are associate to a natural prime of the form 3n + 2. All others have an absolute value equal to 3 or square root of a natural prime of the form 3n + 1. Eisenstein primes in a larger range. If x and y are Eisenstein integers, we say that x divides y if there is some Eisenstein integer z such that ...
If g is a primitive root modulo p, then g is also a primitive root modulo all powers p k unless g p −1 ≡ 1 (mod p 2); in that case, g + p is. [14] If g is a primitive root modulo p k, then g is also a primitive root modulo all smaller powers of p. If g is a primitive root modulo p k, then either g or g + p k (whichever one is odd) is a ...