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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 )
Since no prime number divides 1, p cannot be in the list. This means that at least one more prime number exists that is not in the list. This proves that for every finite list of prime numbers there is a prime number not in the list. [4] In the original work, Euclid denoted the arbitrary finite set of prime numbers as A, B, Γ. [5]
The first five of these numbers – 3, 5, 17, 257, and 65,537 – are prime, [172] but is composite and so are all other Fermat numbers that have been verified as of 2017. [173] A regular n {\displaystyle n} -gon is constructible using straightedge and compass if and only if the odd prime factors of n {\displaystyle n} (if any ...
Not all Euclid numbers are prime. E 6 = 13# + 1 = 30031 = 59 × 509 is the first composite Euclid number. Every Euclid number is congruent to 3 modulo 4 since the primorial of which it is composed is twice the product of only odd primes and thus congruent to 2 modulo 4. This property implies that no Euclid number can be a square.
If n is a power of an odd prime number the formula for the totient says its totient can be a power of two only if n is a first power and n − 1 is a power of 2. The primes that are one more than a power of 2 are called Fermat primes, and only five are known: 3, 5, 17, 257, and 65537. Fermat and Gauss knew of these.
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
In mathematics, particularly in number theory, Hillel Furstenberg's proof of the infinitude of primes is a topological proof that the integers contain infinitely many prime numbers. When examined closely, the proof is less a statement about topology than a statement about certain properties of arithmetic sequences .
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.