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  2. Factorial - Wikipedia

    en.wikipedia.org/wiki/Factorial

    It follows that arbitrarily large prime numbers can be found as the prime factors of the numbers !, leading to a proof of Euclid's theorem that the number of primes is infinite. [35] When n ! ± 1 {\displaystyle n!\pm 1} is itself prime it is called a factorial prime ; [ 36 ] relatedly, Brocard's problem , also posed by Srinivasa Ramanujan ...

  3. Factorial number system - Wikipedia

    en.wikipedia.org/wiki/Factorial_number_system

    The factorial number system is sometimes defined with the 0! place omitted because it is always zero (sequence A007623 in the OEIS). In this article, a factorial number representation will be flagged by a subscript "!". In addition, some examples will have digits delimited by a colon. For example, 3:4:1:0:1:0! stands for

  4. Derangement - Wikipedia

    en.wikipedia.org/wiki/Derangement

    The number of derangements of a set of size n is known as the subfactorial of n or the n th derangement number or n th de Montmort number (after Pierre Remond de Montmort). Notations for subfactorials in common use include !n, D n, d n, or n¡ . [a] [1] [2] For n > 0 , the subfactorial !n equals the nearest integer to n!/e, where n!

  5. 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.

  6. List of mathematical proofs - Wikipedia

    en.wikipedia.org/wiki/List_of_mathematical_proofs

    Bertrand's postulate and a proof; Estimation of covariance matrices; Fermat's little theorem and some proofs; Gödel's completeness theorem and its original proof; Mathematical induction and a proof; Proof that 0.999... equals 1; Proof that 22/7 exceeds π; Proof that e is irrational; Proof that π is irrational

  7. Falling and rising factorials - Wikipedia

    en.wikipedia.org/wiki/Falling_and_rising_factorials

    The falling factorial can be extended to real values of using the gamma function provided and + are real numbers that are not negative integers: = (+) (+) , and so can the rising factorial: = (+) . Calculus

  8. 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 (!

  9. Factorion - Wikipedia

    en.wikipedia.org/wiki/Factorion

    Let be a natural number. For a base >, we define the sum of the factorials of the digits [5] [6] of , :, to be the following: ⁡ = =!. where = ⌊ ⁡ ⌋ + is the number of digits in the number in base , ! is the factorial of and