How can I use pager.setCurrentItem() inside a fragment?

I created many fragments, Fragment1 , Fragment2.. , Fragment50 Inside the first fragment with listener method I want to call Fragment40. But I didnt manage. inside the listener these lines runs

pager.setCurrentItem(0);
pager.setCurrentItem(pager.getCurrentItem() + 1);
pager.setCurrentItem(pager.getCurrentItem() - 1);
But pager.setCurrentItem(40); not run. Gives errors. Any help please?
//First Fragment01
//I want to call Fragment40
public class Frag_2 extends  Fragment implements 
        OnClickListener, AdapterView.OnItemSelectedListener {
//....................................................
public void onActivityCreated(Bundle savedInstanceState) {super.onActivityCreated(savedInstanceState);
final ViewPager pager = (ViewPager) getActivity().findViewById(R.id.pager);
View txtdersHakkinda1 = (View) getActivity().findViewById(R.id.txtDersHakkinda1);
txtdersHakkinda1.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
pager.setCurrentItem(pager.getCurrentItem()+40);    // not run
//  pager.setCurrentItem(0);    //runs
//  pager.setCurrentItem(pager.getCurrentItem() + 1);
//  pager.setCurrentItem(pager.getCurrentItem() - 1);
}
} );    
//......................................................................
}
/////////////////////// If many fragments --> FragmentStatePagerAdapter /////////////
public class MyPagerAdapter extends FragmentStatePagerAdapter {
private List<Fragment> fragments;
public MyPagerAdapter(FragmentManager fm) {
super(fm);
this.fragments = new ArrayList<Fragment>();
fragments.add(new Frag_1<Object>());
fragments.add(new Frag_2());
fragments.add(new Frag_3());
fragments.add(new Frag_4());
 .....................
fragments.add(new Frag_50());
}
@Override
public Fragment getItem(int position) {
return fragments.get(position);
}
@Override
public int getCount() {
return fragments.size();
}
}