A prime number (or a prime) is a natural number greater than 1 that has no positive divisors other than 1 and itself. A natural number greater than 1 that is not a prime number is called a composite number. For example, 5 is prime, as only 1 and 5 divide it, whereas 6 is composite, since it has the divisors 2 and 3 in addition to 1 and 6. The fundamental theorem of arithmetic establishes the central role of primes in number theory: any integer greater than 1 can be expressed as a product of primes that is unique up to ordering. This theorem requires excluding 1 as a prime.

#### Program

package com.scanftree.algos;

public class MyPrimeNumCheck {

public boolean isPrimeNumber(int number) {

for (int i=2; i<=number/2; i++) {

if(number % i == 0) {

return false;

}

}

return true;

}

public static void main(String a[]) {

MyPrimeNumCheck mpc = new MyPrimeNumCheck();

System.out.println("Is 17 prime number? "+mpc.isPrimeNumber(17));

System.out.println("Is 19 prime number? "+mpc.isPrimeNumber(19));

System.out.println("Is 15 prime number? "+mpc.isPrimeNumber(15));

}

}## Output

Is 17 prime number? true

Is 19 prime number? true

Is 15 prime number? false