public static void main(String args[]){
        int input[] = {1,3,6,7,10,11,15};
        ArithemeticProgressionExists ape = new ArithemeticProgressionExists();
        System.out.println(ape.exists(input));
    }
http://www.geeksforgeeks.org/length-of-the-longest-arithmatic-progression-in-a-sorted-array/
src/com/interview/number/ArithemeticProgressionExists.java