indexes are not working for

Dear group,

I have a table foo
anshajdb=# \d foo
Table "public.foo"
Column | Type | Modifiers
---------+-------------------+-----------
snumber | numeric(18,0) |
test | character varying |
Indexes:
"snum_idx" btree (snumber)

when I try to do a query like
explain analyze select * from foo where snumber > 1000;

Seq Scan on foo (cost=0.00..69.00 rows=320 width=391) (actual
time=0.011..0.721 rows=323 loops=1)
Filter: (snumber > 1000::numeric)
Total runtime: 0.979 ms
(3 rows)
It do a sequence scan on table. Why it is not using the snum_idx in this
query. Do I need to change some setting or indexes don't work on this
types of query.

Thanks and Regards
Anshaj

--
"Normal people believe that if it ain't broke, don't
fix it. Engineers believe that if it ain't broke, it
doesn't have enough features yet."