if(giorni_di_differenza <= 15)
{

    try{
        PendingIntent pi = PendingIntent.getActivity(context, 0, new Intent(android.provider.Settings.ACTION_LOCATION_SOURCE_SETTINGS), 0);
        NotificationCompat.Builder n = new NotificationCompat.Builder(context)
            .setContentTitle(nome_evento)
            .setContentText(descrizione_evento)
            .setContentIntent(pi)
            .setAutoCancel(true)
            .setLights(Color.GREEN, 1000, 1000)
            .setSmallIcon(R.drawable.ic_launcher);

        NotificationManager notificationManager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);

        notificationManager.notify(0, n.build());

    }catch(Exception e){
        e.printStackTrace();
    }
}