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A cluster prime is a prime p such that every even natural number k ≤ p − 3 is the difference of two primes not exceeding p. 3, 5, 7, 11, 13, 17, 19, 23, ... (OEIS: A038134) All odd primes between 3 and 89, inclusive, are cluster primes. The first 10 primes that are not cluster primes are: 2, 97, 127, 149, 191, 211, 223, 227, 229, 251.
a lucky prime. [3] the sum of five consecutive primes (7 + 11 + 13 + 17 + 19). a Heegner number. [4] a Pillai prime since 18! + 1 is divisible by 67, but 67 is not one more than a multiple of 18. [5] palindromic in quinary (232 5) and senary (151 6). a super-prime. (19 is prime) an isolated prime. (65 and 69 are not prime) a sexy prime with 61 ...
The existence of arbitrarily large prime gaps can be seen by noting that the sequence ! +,! +, …,! + consists of composite numbers, for any natural number . [67] However, large prime gaps occur much earlier than this argument shows. [68]
One way to classify composite numbers is by counting the number of prime factors. A composite number with two prime factors is a semiprime or 2-almost prime (the factors need not be distinct, hence squares of primes are included). A composite number with three distinct prime factors is a sphenic number. In some applications, it is necessary to ...
Prime number: A positive integer with exactly two positive divisors: itself and 1. The primes form an infinite sequence 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, ... Composite number: A positive integer that can be factored into a product of smaller positive integers. Every integer greater than one is either prime or composite.
The original, called Mersenne's conjecture, was a statement by Marin Mersenne in his Cogitata Physico-Mathematica (1644; see e.g. Dickson 1919) that the numbers were prime for n = 2, 3, 5, 7, 13, 17, 19, 31, 67, 127 and 257, and were composite for all other positive integers n ≤ 257.
Ω(n), the prime omega function, is the number of prime factors of n counted with multiplicity (so it is the sum of all prime factor multiplicities). A prime number has Ω(n) = 1. The first: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37 (sequence A000040 in the OEIS). There are many special types of prime numbers. A composite number has Ω(n) > 1.
Adding 19, however, gives 510529, which is prime. Hence 19 is a Fortunate number. The Fortunate number for p n # is always above p n and all its divisors are larger than p n. This is because p n #, and thus p n # + m, is divisible by the prime factors of m not larger than p n. If a composite Fortunate number does exist, it must be greater than ...