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An even number has the prime factor 2. The first: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24 (sequence A005843 in the OEIS). An odd number does not have the prime ...
Sexagesimal was actually used by the ancient Sumerians and Babylonians, among others; its base, sixty, adds the four convenient factors 4, 12, 20, and 60 to 30 but no new prime factors. The smallest number that has four different prime factors is 210; the pattern follows the primorials. However, these numbers are quite large to use as bases ...
Numbers of the form b n + 1 can only be prime if b is even and n is a power of 2, again assuming n ≥ 2; these are the generalized Fermat numbers, which are Fermat numbers when b = 2. Any factor of a Fermat number 2 2 n + 1 is of the form k2 n+2 + 1.
Duodecimal: Base 12, a numeral system that is convenient because of the many factors of 12. Sexagesimal: Base 60, first used by the ancient Sumerians in the 3rd millennium BC, was passed down to the ancient Babylonians. See positional notation for information on other bases.
As of December 2019 the largest number known to have been factored by a general-purpose algorithm is RSA-240, which has 240 decimal digits (795 bits) and is the product of two large primes. [155] Shor's algorithm can factor any integer in a polynomial number of steps on a quantum computer. [156]
Plot of the number of divisors of integers from 1 to 1000. Highly composite numbers are labelled in bold and superior highly composite numbers are starred. In the SVG file, hover over a bar to see its statistics. Roughly speaking, for a number to be highly composite it has to have prime factors as small
Illustration of the perfect number status of the number 6. In number theory, a perfect number is a positive integer that is equal to the sum of its positive proper divisors, that is, divisors excluding the number itself. For instance, 6 has proper divisors 1, 2 and 3, and 1 + 2 + 3 = 6, so 6 is a perfect number.
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 ...