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A number n that has more divisors than any x < n is a highly composite number (though the first two such numbers are 1 and 2). Composite numbers have also been called "rectangular numbers", but that name can also refer to the pronic numbers, numbers that are the product of two consecutive integers. Yet another way to classify composite numbers ...
Highly composite numbers greater than 6 are also abundant numbers. One need only look at the three largest proper divisors of a particular highly composite number to ascertain this fact. It is false that all highly composite numbers are also Harshad numbers in base 10. The first highly composite number that is not a Harshad number is ...
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 0 or 5 are divisible by 5. [ 11 ] The set of all primes is sometimes denoted by P {\displaystyle \mathbf {P} } (a boldface capital P) [ 12 ] or by P {\displaystyle \mathbb {P} } (a blackboard bold ...
In number theory, a formula for primes is a formula generating the ... 1681, which is equal to 41 × 41, the smallest composite number for this formula for n ≥ ...
Euler's proof of the zeta product formula contains a version of the sieve of Eratosthenes in which each composite number is eliminated exactly once. [9] The same sieve was rediscovered and observed to take linear time by Gries & Misra (1978). [19] It, too, starts with a list of numbers from 2 to n in order. On each step the first element is ...
Rosser and Schoenfeld in Theorem 4, formula 3.14, ... The n-compositorial of a composite number n is the product of all composite numbers up to and including n. [11]
As of 2024, it is known that F n is composite for 5 ≤ n ≤ 32, although of these, complete factorizations of F n are known only for 0 ≤ n ≤ 11, and there are no known prime factors for n = 20 and n = 24. [5] The largest Fermat number known to be composite is F 18233954, and its prime factor 7 × 2 18233956 + 1 was discovered in October 2020.
An alternative and equivalent definition of Carmichael numbers is given by Korselt's criterion.. Theorem (A. Korselt 1899): A positive composite integer is a Carmichael number if and only if is square-free, and for all prime divisors of , it is true that .