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This is a list of articles about prime numbers. A prime number (or prime) is a natural number greater than 1 that has no positive divisors other than 1 and itself. By Euclid's theorem, there are an infinite number of prime numbers. Subsets of the prime numbers may be generated with various formulas for primes.
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.
The number 1 has only a single factor, itself; each prime number has two factors, itself and 1; composite numbers are divisible by at least three different factors. Using the size of the dot representing an integer to indicate the number of factors and coloring prime numbers red and composite numbers blue produces the figure shown.
A factorial prime is a prime number that is one less or one more than a factorial (all factorials greater than 1 are even). [1]The first 10 factorial primes (for n ...
Therefore, every prime number other than 2 is an odd number, and is called an odd prime. [10] Similarly, when written in the usual decimal system, all prime numbers larger than 5 end in 1, 3, 7, or 9. The numbers that end with other digits are all composite: decimal numbers that end in 0, 2, 4, 6, or 8 are even, and decimal numbers that end in ...
This property implies that no Euclid number can be a square. For all n ≥ 3 the last digit of E n is 1, since E n − 1 is divisible by 2 and 5. In other words, since all primorial numbers greater than E 2 have 2 and 5 as prime factors, they are divisible by 10, thus all E n ≥ 3 + 1 have a final digit of 1.
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Euler's theorem states that if n and a are coprime positive integers, then a φ(n) is congruent to 1 mod n. Euler's theorem generalizes Fermat's little theorem. Euler's totient function For a positive integer n, Euler's totient function of n, denoted φ(n), is the number of integers coprime to n between 1 and n inclusive.