Java - first lesson

package firstproject;

import java.util.Scanner;

public class Main {

    static void Pythagoras() {
        double a=3, b=4, c;
        Scanner s = new Scanner(System.in);
        System.out.println("Please input a:");
        a=s.nextDouble();
        System.out.println("Please input b:");
        b=s.nextDouble();
        c=Math.sqrt(a*a + b*b);
        // TODO Auto-generated method stub
        System.out.print("Result="+c);
        s.close();
    }

    static double factorial(double N) {

        double result=1;
        while (N>1) {
            result = result*N;
            N--;
        }
        return result;
    }

    static double fibonacci(double N) {

        double result=0, previous=0, last=1;
        if (N==1) return 1;
        while (N>1) {
            result = last + previous;
            previous = last;
            last = result;
            N--;
        }
        return result;
    }

    static boolean is_prime(int number) {
        //it it is prime, then>
        int N=number/2;
        while (N>1) {
            if (number % N == 0)
                return false;
            N--;
        }
        return true;

    }

    public static void main(String[] args) {
        //homework: use is_prime to print all prime numbers < N,
        // where N is given by user
        System.out.println("is_prime(6)="+is_prime(6));
    }

}