# Is Eratosthenes sieve faster?

## Is Eratosthenes sieve faster?

For finding the sum of prime numbers below 200000, the code below(using sieve of eratosthenes), works much faster, Your code takes nearly 55secs, whereas the code below takes just 0.8secs to execute!

## What is the runtime of the sieve of Eratosthenes?

The classical Sieve of Eratosthenes algorithm takes O(N log (log N)) time to find all prime numbers less than N. In this article, a modified Sieve is discussed that works in O(N) time.

**What is the purpose of Eratosthenes sieve?**

The Sieve of Eratosthenes is a method for finding all primes up to (and possibly including) a given natural . n . This method works well when is relatively small, allowing us to determine whether any natural number less than or equal to is prime or composite.

**What is the best algorithm for finding a prime number?**

Most algorithms for finding prime numbers use a method called prime sieves. Generating prime numbers is different from determining if a given number is a prime or not. For that, we can use a primality test such as Fermat primality test or Miller-Rabin method.

### How is segmented sieve better than simple sieve?

So unlike simple sieve, we don’t check for all multiples of every number smaller than square root of high, we only check for multiples of primes found in step 1. And we don’t need O(high) space, we need O(sqrt(high) + n) space.

### How did Eratosthenes measure the size of the Earth?

In the third century BCE , Eratosthenes, a Greek librarian in Alexandria , Egypt , determined the earth’s circumference to be 40,250 to 45,900 kilometers (25,000 to 28,500 miles) by comparing the Sun’s relative position at two different locations on the earth’s surface.

**What is the fastest known deterministic method in the world for primality testing?**

Fast deterministic tests The first deterministic primality test significantly faster than the naive methods was the cyclotomy test; its runtime can be proven to be O((log n)c log log log n), where n is the number to test for primality and c is a constant independent of n.

**How is the segmented Sieve better than a simple Sieve?**

## Who invented sieve of Eratosthenes?

Sieve of Eratosthenes is an almost mechanical procedure for separating out composite numbers and leaving the primes. It was invented by the Greek scientist and mathematician Eratosthenes who lived approximately 2,300 years ago.

## What did Eratosthenes do wrong?

If you take the lowest estimate attributed to Eratosthenes, his error was less than one percent—a phenomenal calculation. Eratosthenes determined the earth’s size by observing known phenomena and applying basic arithmetic and geometry to them.

**How did Eratosthenes calculate 7 Degrees?**

Eratosthenes could measure the angle of the Sun’s rays off the vertical by dividing the length of the leg opposite the angle (the length of the shadow) by the leg adjacent to the angle (the height of the pole). This gave him an angle of 7.12 degrees.

**What is the trick to remember prime numbers?**

Add up the two digits of a number to tell if it’s divisible by three, and that leaves only numbers divisible by seven (and not by 2 or 3 or 5), which are very easy to memorize: 7, 49, 77, and 91.

### Are primes predictable?

Although whether a number is prime or not is pre-determined, mathematicians don’t have a way to predict which numbers are prime, and so tend to treat them as if they occur randomly.

### What is Atkin’s sieve?

Atkin’s Sieve is improvement over Eratosthenes. Instead of looping through all the number to find out it is prime or not, it relies on quadratic equation and modulo 60 to find the patterns of prime/no prime and mark them in boolean array.

**How does the sieve of Eratosthenes work?**

Compared with the ancient Sieve of Eratosthenes, which marks off multiples of primes, it does some preliminary work and then marks off multiples of squares of primes, that’s why it has a better theoretical asymptotic complexity with Complexity of (N / (log log N)) Create a results list, filled with 2, 3, and 5.

**What is the ratio of sieving to sieving range?**

From an actual implementation of the algorithm, the ratio is about 0.25 for sieving ranges as low as 67.