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  2. Twin prime - Wikipedia

    en.wikipedia.org/wiki/Twin_prime

    Twin prime. A twin prime is a prime number that is either 2 less or 2 more than another prime number—for example, either member of the twin prime pair (17, 19) or (41, 43). In other words, a twin prime is a prime that has a prime gap of two. Sometimes the term twin prime is used for a pair of twin primes; an alternative name for this is prime ...

  3. Prime gap - Wikipedia

    en.wikipedia.org/wiki/Prime_gap

    A prime gap is the difference between two successive prime numbers. The n -th prime gap, denoted gn or g ( pn) is the difference between the ( n + 1)-st and the n -th prime numbers, i.e. We have g1 = 1, g2 = g3 = 2, and g4 = 4. The sequence ( gn) of prime gaps has been extensively studied; however, many questions and conjectures remain unanswered.

  4. 137 (number) - Wikipedia

    en.wikipedia.org/wiki/137_(number)

    the 33rd prime number; the next is 139, with which it comprises a twin prime, and thus 137 is a Chen prime. [ 1 ] an Eisenstein prime with no imaginary part and a real part of the form 3 n − 1 {\displaystyle 3n-1} .

  5. Brun's theorem - Wikipedia

    en.wikipedia.org/wiki/Brun's_theorem

    The convergence to Brun's constant. In number theory, Brun's theorem states that the sum of the reciprocals of the twin primes (pairs of prime numbers which differ by 2) converges to a finite value known as Brun's constant, usually denoted by B2 (sequence A065421 in the OEIS ). Brun's theorem was proved by Viggo Brun in 1919, and it has ...

  6. Prime number - Wikipedia

    en.wikipedia.org/wiki/Prime_number

    A prime number (or a prime) is a natural number greater than 1 that is not a product of two smaller natural numbers. A natural number greater than 1 that is not prime is called a composite number. For example, 5 is prime because the only ways of writing it as a product, 1 × 5 or 5 × 1, involve 5 itself. However, 4 is composite because it is a ...

  7. Mental calculation - Wikipedia

    en.wikipedia.org/wiki/Mental_calculation

    Likewise, 14 is a multiple of 2, so the product should be even. Furthermore, any number which is a multiple of both 5 and 2 is necessarily a multiple of 10, and in the decimal system would end with a 0. The correct answer is 210. It is a multiple of 10, 7 (the other prime factor of 14) and 3 (the other prime factor of 15).

  8. List of prime numbers - Wikipedia

    en.wikipedia.org/wiki/List_of_prime_numbers

    All prime numbers from 31 to 5,131,135,981 for free download. Lists of Primes at the Prime Pages. The Nth Prime Page Nth prime through n=10^12, pi(x) through x=3*10^13, Random prime in same range. Prime Numbers List Full list for prime numbers below 10,000,000,000, partial list for up to 400 digits.

  9. Lucky number - Wikipedia

    en.wikipedia.org/wiki/Lucky_number

    Lucky number. In number theory, a lucky number is a natural number in a set which is generated by a certain "sieve". This sieve is similar to the Sieve of Eratosthenes that generates the primes, but it eliminates numbers based on their position in the remaining set, instead of their value (or position in the initial set of natural numbers). [1]