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Fortunate numbers: 3, 5, 7, 13, 23, 17, 19, 23, 37, 61, ... The smallest integer m > 1 such that p n # + m is a prime number, where the primorial p n # is the product of the first n prime numbers. A005235: Semiperfect numbers: 6, 12, 18, 20, 24, 28, 30, 36, 40, 42, ... A natural number n that is equal to the sum of all or some of its proper ...
Using this approach, Meissel computed π(x), for x equal to 5 × 10 5, 10 6, 10 7, and 10 8. In 1959, Derrick Henry Lehmer extended and simplified Meissel's method. Define, for real m and for natural numbers n and k, P k (m,n) as the number of numbers not greater than m with exactly k prime factors, all greater than p n. Furthermore, set P 0 (m ...
These sequences of natural numbers can again be represented by single natural numbers, facilitating their manipulation in formal theories of arithmetic. Since the publishing of Gödel's paper in 1931, the term "Gödel numbering" or "Gödel code" has been used to refer to more general assignments of natural numbers to mathematical objects.
One of the simplest and most natural examples is the multiset of prime factors of a natural number n. Here the underlying set of elements is the set of prime factors of n . For example, the number 120 has the prime factorization 120 = 2 3 3 1 5 1 , {\displaystyle 120=2^{3}3^{1}5^{1},} which gives the multiset {2, 2, 2, 3, 5} .
In Set, the category of sets, the standard natural numbers are an NNO. [6] A terminal object in Set is a singleton, and a function out of a singleton picks out a single element of a set. The natural numbers 𝐍 are an NNO where z is a function from a singleton to 𝐍 whose image is zero, and s is the successor function.
Graph of the number of primes ending in 1, 3, 7, and 9 up to n for n < 10 000. Another example is the distribution of the last digit of prime numbers. Except for 2 and 5, all prime numbers end in 1, 3, 7, or 9. Dirichlet's theorem states that asymptotically, 25% of all primes end in each of these four digits.
For every real number , there is a natural number such that for every natural number , we have <; that is, the sequence terms are eventually smaller than any fixed . Symbolically, this is: ∀ K ∈ R ( ∃ N ∈ N ( ∀ n ∈ N ( n ≥ N x n < K ) ) ) {\displaystyle \forall K\in \mathbb {R} \left(\exists N\in \mathbb {N} \left(\forall n\in ...
An abundant number is a natural number n for which the sum of divisors σ(n) satisfies σ(n) > 2n, or, equivalently, the sum of proper divisors (or aliquot sum) s(n) satisfies s(n) > n. The abundance of a natural number is the integer σ(n) − 2n (equivalently, s(n) − n).