For the last archived sequence, use the following:

SQL> SELECT MAX(SEQUENCE#) FROM V$ARCHIVED_LOG;
MAX(SEQUENCE#)
--------------
 145

For the last applied sequence, use the following:

SQL> SELECT MAX(SEQUENCE#) FROM V$ARCHIVED_LOG WHERE APPLIED='YES';
MAX(SEQUENCE#)
--------------
 144

From the preceding two queries, we see that the latest sequence, 145, is being archived or written into the standby redo logfiles. There's expected to be a lag of one sequence between archived and applied columns.

SQL> SELECT SEQUENCE#,APPLIED FROM V$ARCHIVED_LOG ORDER BY SEQUENCE#;

 SEQUENCE# APPLIED
---------- ---------
 140 YES
 141 YES
 142 YES
 143 YES
 144 YES
 145 IN-MEMORY

The log sequence 145 is still being shipped.

SQL> SELECT MAX(SEQUENCE#) FROM V$ARCHIVED_LOG;
MAX(SEQUENCE#)
--------------
 145

Perform log switches several times and check.

SQL> alter system switch logfile;
System altered.

SQL> SELECT MAX(SEQUENCE#) FROM V$ARCHIVED_LOG;
MAX(SEQUENCE#)
--------------
 148

SQL> SELECT SEQUENCE#,APPLIED FROM V$ARCHIVED_LOG ORDER BY SEQUENCE#;
 SEQUENCE# APPLIED
---------- ---------
 143 YES
 144 YES
 145 YES
 146 YES
 147 YES
 148 YES

The APPLIED column on standby will be very helpful to determine which sequence is generated and which sequences are applied. In the previous scenario, the archives generated on primary and archives applied on standby have the same sequence number; hence, standby is synchronized with the primary database.

The value of the APPLIED column for the most recently received logfile will be IN-MEMORY, or YES if that logfile has been applied.