Column DEGREE of the DBA_INDEXES view is VARCHAR type

Not aware DEGREE is VARCHAR2(40) type. So surprised to see the following error. It appears that some values can not be converted to numbers.

system@DB10G> select index_name, degree from dba_indexes where degree > 2;
select index_name, degree from dba_indexes where degree > 2
                                                 *
ERROR at line 1:
ORA-01722: invalid number


system@DB10G> select index_name, degree from all_indexes where degree > 2;
select index_name, degree from all_indexes where degree > 2
                                                 *
ERROR at line 1:
ORA-01722: invalid number


system@DB10G> select index_name, degree from user_indexes where degree > 2;




system@DB10G> desc dba_indexes;
 Name                                    Null?    Type
 ------------------------------------ -------- ---------------
 OWNER                                NOT NULL VARCHAR2(30)
 INDEX_NAME                           NOT NULL VARCHAR2(30)
 INDEX_TYPE                                    VARCHAR2(27)
 NEXT_EXTENT                                   NUMBER
 MIN_EXTENTS                                   NUMBER
 AVG_DATA_BLOCKS_PER_KEY                       NUMBER
 CLUSTERING_FACTOR                             NUMBER
 STATUS                                        VARCHAR2(8)
     .....
 NUM_ROWS                                      NUMBER
 SAMPLE_SIZE                                   NUMBER
 LAST_ANALYZED                                 DATE
 DEGREE                                        VARCHAR2(40)
 INSTANCES                                     VARCHAR2(40)
 PARTITIONED                                   VARCHAR2(3)
 BUFFER_POOL                                   VARCHAR2(7)
 USER_STATS                                    VARCHAR2(3)
 DURATION                                      VARCHAR2(15)
     .....
 FUNCIDX_STATUS                                VARCHAR2(8)
 JOIN_INDEX                                    VARCHAR2(3)
 IOT_REDUNDANT_PKEY_ELIM                       VARCHAR2(3)
 DROPPED                                       VARCHAR2(3)

system@DB10G>