Prime number sequence

What is the Prime Number?

A prime number is a special natural number. It has exactly two divisors – 1 and itself.

How to find a prime number?

• Take the root of the number to be examined
• Note which prime numbers exist so far
• Apply these prime numbers to the original number and see if they divide without a remainder.
• If no number is found until then, it is a prime number.

Output of prime numbers

import java.util.Scanner;

public class PrimeAlgorithm {

	private static int primeAlgorithm(int number) {
		int counter = 0;

		for (int i = 1; i <= number; i++) {
			if (number % i == 0) {
				counter += 1;
			}
		}

		if (counter == 2) {
			return number;
		} else {
			return 0;
		}
	}

	public static void main(String[] args) {
		Scanner reader = new Scanner(System.in);

		System.out.print("Enter upper limit of prime numbers: ");
		int number = reader.nextInt();
		reader.close();

		for (int i = 1; i <= number; i++) {
			if (primeAlgorithm(i) != 0) {
				System.out.println(primeAlgorithm(i));
			}
		}
	}
}

Output

Enter upper limit of prime numbers: 50
2
3
5
7
11
13
17
19
23
29
31
37
41
43
47

Check if number is prime number

import java.util.Scanner;

public class PrimeAlgorithm {

	private static boolean isPrime(int number) {
		if (number <= 1)
			return false;

		for (int i = 2; i <= number / 2; ++i) {
			if (number % i == 0) {
				return false;
			}
		}

		return true;
	}

	public static void main(String[] args) {
		Scanner reader = new Scanner(System.in);

		System.out.print("Enter a number to check whether it is a prime number: ");
		int number = reader.nextInt();
		reader.close();

		if (isPrime(number)) {
			System.out.println(number + " is a prime number!");
		} else {
			System.out.println(number + " is not a prime number!");
		}
	}
}

Output

Enter a number to check whether it is a prime number: 31
31 is a prime number!