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Eratosthenes' method of finding prime and composite number is called 'The Sieve of Eratosthene'.

Q: What is the name of Eratosthenes' method of finding composite numbers?

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when i did this problem i was doing a eratosthenes sieve method and the numbers was from 1-100 so i got the longest string of consecutive composite numbers on the grid are 74-82 this should be right. BTW I'm 13 doing my moms college work Sorry, but 79 is a prime number. I got 90~96

First of all, every number is a factor - of its multiples.There is no general way to distinguish between prime and composite numbers. At one level, though, there are some simple ways. If the number is not 2, but ends in 0, 2, 4, 6 or 8 then it is a composite, If the number is not 5 but ends in 0 or 5 it is composite. If the number is not 3 but the sum of all the digits of a number is 3 or divisible by 3, then it is composite. There are moderately complicated divisibility rules for 7 and 11. But this method does not identify all composite numbers and there is no guaranteed method.

If you have two numbers A and B, and A > B, then GCF(A, B) = (A-B, B) Thus the problem of finding the GCF of A and B has been reduced to finding the GCF of B and a smaller number, A-B. This process can be continued until the two numbers are the same: and that number is the GCF.

The sieve is just a method for finding primes. You write down the numbers 2 through n (lets say n = 100). And you go through the list crossing off numbers in a set way. You start with 2, and cross off 4,6,8,10, etc etc, all the way to 100. Then you go to 3, and cross off 6,9,12,15, etc all the way to 100. Then you go to the next number (four has already been crossed off when you did 2 so we're at 5 now), cross off 10,15,20,25, etc.. all the way to 100, etc etc etc through the list till you do the last one at n/2 (50). What you have in front of you now is a list of all the prime numbers from 2 to n (100), since everything else that is composite (not prime), has been crossed out.

Since prime numbers only have one prime factor (themselves), factor trees are unnecessary.

Related questions

Eratosthenes

It is called a sieve.

One method for finding prime numbers is called the "Sieve of Eratosthenes" because it basically "sifts" through the numbers looking for numbers that are not not prime.

The method of sieving the multiples of prime numbers until only the prime numbers remain, while attributed to Eratosthenes, is originally thought to have been the work of Nicomachus.

Eratosthenes created a sieve that will do that.

when i did this problem i was doing a eratosthenes sieve method and the numbers was from 1-100 so i got the longest string of consecutive composite numbers on the grid are 74-82 this should be right. BTW I'm 13 doing my moms college work Sorry, but 79 is a prime number. I got 90~96

It is a semi-prime, which is a product of two prime numbers.

If a number has more than two factors, it's composite.

About 276 BC Eratosthenes was a Greek mathematician who is credited with a simple method of making a list of as many primes as you wish. His method is known as the Sieve of Eratosthenes.

prime numbers

To find a composite number, check if the number can be divided by 2,3,4,5, ect. If it can, it`s composite. If not, it`s prime.

The method know as The sieve of Eratosthenes is the easiest method. you simply write down all the numbers from 1 to 100 in rows of 10 and then you go through and you mark out all of the multiples of 2,3,4,5,6,7,8,9,10