1. Sum of natural numbers class SumOfNaturalNumbers {
public static void main (String arg[]) {
int m = 3, n = 10;
if (m > n) {
System.out.println (“Invalid input!”); }
else {
System.out.println (“Sum of numbers from ” + m + “ to ” + n + “ is ” + Sum(m, n));

2. Sum of natural numbers public static int Sum (int m, int n) {
int x, y;
if (m==n) return m;
x = Sum(m, (m+n)/2);
y = Sum((m+n)/2+1, n);
return (x+y); }
} // end class

3. Fibonacci series class fib { public static long fibonacci(long n){
if (n==1) fib = 0;
else if (n==2) fib = 1;
else fib = fibonacci(n-1) + fibonacci(n-2);
return fib; }
public static void main (String args[]) {
long i, x;
long n = 17;
for (i=1; i<=n; i++) {
x = fibonacci(i);
System.out.println(x);