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  2. Natural density - Wikipedia

    en.wikipedia.org/wiki/Natural_density

    A subset A of positive integers has natural density α if the proportion of elements of A among all natural numbers from 1 to n converges to α as n tends to infinity.. More explicitly, if one defines for any natural number n the counting function a(n) as the number of elements of A less than or equal to n, then the natural density of A being α exactly means that [1]

  3. Dirichlet's theorem on arithmetic progressions - Wikipedia

    en.wikipedia.org/wiki/Dirichlet's_theorem_on...

    In number theory, Dirichlet's theorem, also called the Dirichlet prime number theorem, states that for any two positive coprime integers a and d, there are infinitely many primes of the form a + nd, where n is also a positive integer.

  4. Roth's theorem on arithmetic progressions - Wikipedia

    en.wikipedia.org/wiki/Roth's_Theorem_on...

    Roth's theorem on arithmetic progressions (infinite version): A subset of the natural numbers with positive upper density contains a 3-term arithmetic progression. An alternate, more qualitative, formulation of the theorem is concerned with the maximum size of a Salem–Spencer set which is a subset of [ N ] = { 1 , … , N } {\displaystyle [N ...

  5. Catalan number - Wikipedia

    en.wikipedia.org/wiki/Catalan_number

    When this portion of the path is reflected, it will have one more up step than right steps. Since there are still 2 n steps, there are now n + 1 up steps and n − 1 right steps. So, instead of reaching ( n , n ) , all bad paths after reflection end at ( n − 1, n + 1) .

  6. Number theory - Wikipedia

    en.wikipedia.org/wiki/Number_theory

    Number theory is a branch of pure mathematics devoted primarily to the study of the integers and arithmetic functions.German mathematician Carl Friedrich Gauss (1777–1855) said, "Mathematics is the queen of the sciences—and number theory is the queen of mathematics."

  7. Presburger arithmetic - Wikipedia

    en.wikipedia.org/wiki/Presburger_arithmetic

    This means it is possible to algorithmically determine, for any sentence in the language of Presburger arithmetic, whether that sentence is provable from the axioms of Presburger arithmetic. The asymptotic running-time computational complexity of this algorithm is at least doubly exponential, however, as shown by Fischer & Rabin (1974).

  8. Elliptical distribution - Wikipedia

    en.wikipedia.org/wiki/Elliptical_distribution

    In the 2-dimensional case, if the density exists, each iso-density locus (the set of x 1,x 2 pairs all giving a particular value of ()) is an ellipse or a union of ellipses (hence the name elliptical distribution). More generally, for arbitrary n, the iso-density loci are unions of ellipsoids. All these ellipsoids or ellipses have the common ...

  9. Lexical density - Wikipedia

    en.wikipedia.org/wiki/Lexical_density

    Lexical density is a concept in computational linguistics that measures the structure and complexity of human communication in a language. [1] Lexical density estimates the linguistic complexity in a written or spoken composition from the functional words (grammatical units) and content words (lexical units, lexemes ).