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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]
M 4,423 was the first prime discovered with more than 1000 digits, M 44,497 was the first with more than 10,000, and M 6,972,593 was the first with more than a million. In general, the number of digits in the decimal representation of M n equals ⌊n × log 10 2⌋ + 1, where ⌊x⌋ denotes the floor function (or equivalently ⌊log 10 M n ...
f p+1 ≡ 0 (mod p), where f k is the k-th Fibonacci number. The first condition is the Fermat primality test using base 2. In general, if p ≡ a (mod x 2 +4), where a is a quadratic non-residue (mod x 2 +4) then p should be prime if the following conditions hold: 2 p−1 ≡ 1 (mod p), f(1) p+1 ≡ 0 (mod p), f(x) k is the k-th Fibonacci ...
As of 2024, it is known that F n is composite for 5 ≤ n ≤ 32, although of these, complete factorizations of F n are known only for 0 ≤ n ≤ 11, and there are no known prime factors for n = 20 and n = 24. [5] The largest Fermat number known to be composite is F 18233954, and its prime factor 7 × 2 18233956 + 1 was discovered in October 2020.
Usually, the meaning of x ′ is defined when it is first used, but sometimes, its meaning is assumed to be understood: A derivative or differentiated function: in Lagrange's notation, f ′ (x) and f ″(x) are the first and second derivatives of f (x) with respect to x. Likewise for f ‴(x) and f ⁗(x).
A prime divides if and only if p is congruent to ±1 modulo 5, and p divides + if and only if it is congruent to ±2 modulo 5. (For p = 5, F 5 = 5 so 5 divides F 5) . Fibonacci numbers that have a prime index p do not share any common divisors greater than 1 with the preceding Fibonacci numbers, due to the identity: [6]
In Python 3, x / y performs "true division", meaning that it always returns a float, even if both x and y are integers that divide evenly. >>> 4 / 2 2.0 and // performs integer division or floor division , returning the floor of the quotient as an integer.