Encoding and result string length

Dear Friends,

Postgres 7.3.2 on Linux 8

I would like to fetch the datas from a table in a encoded format.

create table encodeco(c1 int4, c2 int4);
insert into encodeco values(10000, 20000);
select * from encodeco;

So I want to encode the data while selecting.
select encode(c1,'base64') from encodeco;

ERROR: Function encode(integer, "unknown") does not exist
Unable to identify a function that satisfies the given argument types
You may need to add explicit typecasts

So i tried
select encode('c1','base64') from encodeco;

I got a result as
1 YzE=

But this is the encoded value for 'c1' and not for the value 10000.

Please shed some light.

Also is it possible to get the encoded values with only 2 charactors, irrespective of the values of c1 ranging from 100 to 10 million

Thanks
Kumar