# Write a program to find out prime no from 1 to 100 in java

Finding All Prime Numbers in the Range of 2 and N Problem Statement In a previous examplewe have discussed how to determine if a positive integer is a prime number. Sieve of Eratosthenes Algorithm to generate Prime numbers upto in Java There are many occasions when you need to generate all prime numbers upto a specified integer and one algorithm which is most often used to generate prime numbers is Sieve of Eratosthenes.

Its an ancient greek algorithm to find all prime numbers upto a given number and named after the famous greek mathematician Eratosthenes. He was the first man to calculate the circumference of the earth and also known for working on calendars with leap years.

A prime number is a whole number which is either divisible by 1 or itself e. You can see they are not divisible to any positive whole integer. In other words, prime number doesn't have a factor other than 1 or itself. You can use this algorithm to generate prime numbers from 1 to or up-to any maximum value.

In this tutorial, we will not only learn how Sieve of Eratosthenes algorithm works but also we will generate prime numbers using this algorithm and verify whether all number generated are actually prime or not.

You create an array of larger than 1 by specified integer, so that index of array represent the actual integer stored on it. Then you start with 2, because 0 and 1 are not considered prime. A prime number is either divisible by 1 or by itself, it doesn't have any other factor.

Since 2 is a prime number, we mark this as prime and cross out all its multiple because they won't be prime, Why? In order to cross all numbers which are multiple by 2, we just skip our array counter by 2, which means 2, 4, 6, 8 all are multiples of 2 and they well be crossed. Next number in the array is 3, now 3 is also not divisible by anyone so its a prime and we mark it as prime and again crossed out all multiples of 3 becasue they won't be prime. In order to cross out multiples of 3, we skip array counter by 3, which means 3, 9, 12, 15 all are crossed.

Now, Next number is 4 but its already crossed because it was multiple of 2 so we skip to next number which is 5. Again 5 is a prime number so we mark it as prime and cross out all numbers which are multiple of 5, because they won't be prime as they are divisible by 5.

## Java Numbers Exercises - w3resource

In order to cross all multiples of 5, we just increase array counter by 5, so numbers like 10, 15, 20, 25 will be crossed out. We continue this process until we reach at the square root of given number, because every multiple in the array has a prime factor that is less than or equal to the square root of the given number, so we don't have to cross out multiples of numbers larger than that root.

For example, in order to find all prime numbers between 1 toits enough to check until Test; import static org. This is a very efficient algorithm to generate large number of prime numbers and can be used to solve complex programming problems where you need an array of prime numbers.urbanagricultureinitiative.comtream - stores information about the connection between an input device and the computer or program.

urbanagricultureinitiative.comr - used to read the input available from an InputStream object. The Scanner class has a method called nextLine that returns a line of text as typed by the user. Finding All Prime Factors of a Positive Integer Problem Statement.

As we have learned in high school, any positive integer can be factorized into prime factors.

## Sieve of Eratosthenes Algorithm to generate Prime numbers upto in Java

For example, can be factorized as follows: Thus, has factors 2, 3, 5, 5,, 7, 7, 13, 17, 19 and Note that all factors are prime . there some lib function are used, but need mathematical logic for urbanagricultureinitiative.com Like multiplication is consecutive addition of numbers.

Aug 07,  · C program to print Prime Numbers Between 1 and n Check out programming video tutorials on this YOUTUBE Channel. Reply Delete. Replies. Reply. sarbjeet khosa 26 April at C program to print Prime Numbers Between 1 and n; C program to print the Prime . 1st Java Program OOPS Concepts Class Object Abstraction Encapsulation Polymorphism Inheritance int b = 1; int c = 0; c = start; urbanagricultureinitiative.comn(" The Fibonacci Series are: "); while (c The Fibonacci Series are: 11 12 23 35 58 93 D.

Set Starting value and N times to Fibonacci Series. An emirp (prime spelled backward) is a nonpalindromic prime number whose reversal is also a prime. For example, 17 is a prime and 71 is a prime. So, 17 and 71 are emirps. Write a program that displays the first emirps. Display 10 numbers per line and align the numbers properly.

C Program to Check Whether a Number is Prime or Not