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  2. Double factorial - Wikipedia

    en.wikipedia.org/wiki/Double_factorial

    These are counted by the double factorial 15 = (6 − 1)‼. In mathematics, the double factorial of a number n, denoted by n‼, is the product of all the positive integers up to n that have the same parity (odd or even) as n. [1] That is,

  3. Formula for primes - Wikipedia

    en.wikipedia.org/wiki/Formula_for_primes

    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]

  4. Wilson's theorem - Wikipedia

    en.wikipedia.org/wiki/Wilson's_theorem

    In algebra and number theory, Wilson's theorem states that a natural number n > 1 is a prime number if and only if the product of all the positive integers less than n is one less than a multiple of n.

  5. PrimeGrid - Wikipedia

    en.wikipedia.org/wiki/PrimeGrid

    In the summer of 2007, the Cullen and Woodall prime searches were launched. In the Fall, more prime searches were added through partnerships with the Prime Sierpinski Problem and 3*2^n-1 Search projects. Additionally, two sieves were added: the Prime Sierpinski Problem combined sieve which includes supporting the Seventeen or Bust sieve and the ...

  6. Factorial - Wikipedia

    en.wikipedia.org/wiki/Factorial

    Legendre's formula describes the exponents of the prime numbers in a prime factorization of the factorials, and can be used to count the trailing zeros of the factorials. Daniel Bernoulli and Leonhard Euler interpolated the factorial function to a continuous function of complex numbers, except at the negative integers, the (offset) gamma function.

  7. Legendre's formula - Wikipedia

    en.wikipedia.org/wiki/Legendre's_formula

    Since ! is the product of the integers 1 through n, we obtain at least one factor of p in ! for each multiple of p in {,, …,}, of which there are ⌊ ⌋.Each multiple of contributes an additional factor of p, each multiple of contributes yet another factor of p, etc. Adding up the number of these factors gives the infinite sum for (!

  8. Factorial prime - Wikipedia

    en.wikipedia.org/wiki/Factorial_prime

    (resulting in 24 factorial primes - the prime 2 is repeated) No other factorial primes are known as of December 2024 [update] . When both n ! + 1 and n ! − 1 are composite , there must be at least 2 n + 1 consecutive composite numbers around n !, since besides n ! ± 1 and n ! itself, also, each number of form n ! ± k is divisible by k for 2 ...

  9. Stirling's approximation - Wikipedia

    en.wikipedia.org/wiki/Stirling's_approximation

    Comparison of Stirling's approximation with the factorial In mathematics , Stirling's approximation (or Stirling's formula ) is an asymptotic approximation for factorials . It is a good approximation, leading to accurate results even for small values of n {\displaystyle n} .