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In mathematics, the prime-counting function is the function counting the number of prime numbers less than or equal to some real number x. [1] [2] It is denoted by π(x) (unrelated to the number π). A symmetric variant seen sometimes is π 0 (x), which is equal to π(x) − 1 ⁄ 2 if x is exactly a prime number, and equal to π(x) otherwise.
Because the set of primes is a computably enumerable set, by Matiyasevich's theorem, it can be obtained from a system of Diophantine equations. Jones et al. (1976) found an explicit set of 14 Diophantine equations in 26 variables, such that a given number k + 2 is prime if and only if that system has a solution in nonnegative integers: [7]
In number theory, Euler's totient function counts the positive integers up to a given integer n that are relatively prime to n. It is written using the Greek letter phi as φ ( n ) {\displaystyle \varphi (n)} or ϕ ( n ) {\displaystyle \phi (n)} , and may also be called Euler's phi function .
A more recent "elementary" proof of the prime number theorem uses ergodic theory, due to Florian Richter. [28] The prime number theorem is obtained there in an equivalent form that the Cesàro sum of the values of the Liouville function is zero.
A prime sieve or prime number sieve is a fast type of algorithm for finding primes. There are many prime sieves. The simple sieve of Eratosthenes (250s BCE), the sieve of Sundaram (1934), the still faster but more complicated sieve of Atkin [1] (2003), sieve of Pritchard (1979), and various wheel sieves [2] are most common.
In 1737, Euler related the study of prime numbers to what is known now as the Riemann zeta function: he showed that the value () reduces to a ratio of two infinite products, Π p / Π (p–1), for all primes p, and that the ratio is infinite. [1] [2] In 1775, Euler stated the theorem for the cases of a + nd, where a = 1. [3]
Pr(a): a is a prime number Pr(a) = def a>1 & NOT(Exists c) 1<c<a [ c|a ] p i: the i+1th prime number (a) i: exponent of p i in a: the unique x such that p i x |a & NOT(p i x' |a) lh(a): the "length" or number of non-vanishing exponents in a; lo(a, b): (logarithm of a to base b): If a, b > 1 then the greatest x such that b x | a else 0
In number theory, the prime omega functions and () count the number of prime factors of a natural number . Thereby (little omega) counts each distinct prime factor, whereas the related function () (big omega) counts the total number of prime factors of , honoring their multiplicity (see arithmetic function).