Oracle sequence for a primary key field doesn'

I have the following code that attempts to fetch a generated sequence value for the primary key column COUNTRY_ID of the COUNTRY table in my Oracle (10g) database.

Country c=new Country();

c.setCountryName(request.getParameter("txtCountryName"));
c.setCountryCode(request.getParameter("txtCountryCode"));
Zone z=(Zone) session.get(Zone.class, new BigDecimal(request.getParameter("zoneId")));
c.setZone(z);
session.save(c);

session.flush();
//session.refresh(c);
System.out.println(c.getCountryId()); //Attempts to display the sequence value.
session.getTransaction().commit();

This statement System.out.println(c.getCountryId()); in this codes attempts to display the currently generated sequence value after insertion is done.

Sequence generated values in the Oracle table are inserted ~~in multiple of 2 i.e~~ something like this 414, 416, 418, 420... instead of being inserted them in a chain like 414, 415, 416, 417, 418, 419, 420...

Suppose, the currently inserted sequence value in the Oracle table is 426, this statement System.out.println(c.getCountryId()); shows 425 (whereas in the COUNTRY_ID column in the Oracle table, the inserted value is 426).

Presumably, it appears that the sequence is executed twice for some reasons.

In my Hibernate POJO, I have designated the countryId primary key column as follows,

@Id
@Column(name = "COUNTRY_ID")
@SequenceGenerator(name = "CountryIdSequence", sequenceName = "COUNTRY_SEQ")
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "CountryIdSequence")
private long countryId;

In the Country.hbm.xml mapping file, this column countryId is mapped as follows.

<id name="countryId" type="long">
  <column name="COUNTRY_ID" precision="35" scale="0"/>
  <generator class="sequence">
    <param name="sequence">COUNTRY_SEQ</param>
  </generator>
</id>

What am I missing here?

I indeed had a trigger against the COUNTRY table which is automatically created by an Oracle GUI tool to associate the sequence with the primary key column COUNTRY_ID.

The sequence was being executed twice once by Hibernate and again by the trigger. I disabled the trigger temporarily and the approach worked as intended.