postgres=#  begin;
BEGIN
postgres=# create table a (i serial);
CREATE TABLE
postgres=# \d a
                            Table "public.a"
 Column |  Type   | Collation | Nullable |           Default            
--------+---------+-----------+----------+------------------------------
 i      | integer |           | not null | nextval('a_i_seq'::regclass)

postgres=# alter sequence a_i_seq rename to a_i_seq_new;
ALTER SEQUENCE
postgres=# \d a
                              Table "public.a"
 Column |  Type   | Collation | Nullable |             Default              
--------+---------+-----------+----------+----------------------------------
 i      | integer |           | not null | nextval('a_i_seq_new'::regclass)