Generate sequence rowid for chunk

Hello. Help me to distribute records on CHUNK across the field of ROWID. Why at me such results turn out?

$ sqlplus / as sysdba

SQL*Plus: Release 12.1.0.2.0 Production on Tue Nov 21 11:40:32 2017

Copyright (c) 1982, 2014, Oracle.  All rights reserved.

Connected to:

Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production

With the Partitioning, OLAP, Advanced Analytics, Real Application Testing

and Unified Auditing options

TRNZT> select rowid from a4m_twcms.tcard WHERE rownum<10;

ROWID

------------------

AAAXIYAAOAAD7VPAAa

AAAXIYAASAADcJfAAC

AAAXIYAASAAEH+IAAB

AAAXIYAASAAEH9UAAR

AAAXIYAAUAADYvVAAg

AAAXIYAASAAEJe8AAP

AAAXIYAASAAEJMEAAT

AAAXIYAASAAD/9NAAV

AAAXIYAATAAECXsAAN

9 rows selected.

TRNZT> select count(*) from a4m_twcms.tcard WHERE rowid BETWEEN 'AAAXIYAAOAAD7VPAAa' AND 'AAAXIYAATAAECXsAAN';