My test:

create sequence seq_test start with 1 increment by 1 cache 20;
select seq_test.nextval from dual;
1

SEQUENCE_NAME NEXTVALUE MIN_VALUE CACHE_SIZE HIGHWATER
--------------- ---------- ---------- ---------- ---------
SEQ_TEST 2 1 20 21

select seq_test.nextval from dual;
2

SEQUENCE_NAME NEXTVALUE MIN_VALUE CACHE_SIZE HIGHWATER
--------------- ---------- ---------- ---------- ---------
SEQ_TEST 3 1 20 21

select seq_test.nextval from dual;
3

SEQUENCE_NAME NEXTVALUE MIN_VALUE CACHE_SIZE HIGHWATER
--------------- ---------- ---------- ---------- ---------
SEQ_TEST 4 1 20 21

SQL> shutdown abort;
SQL> startup;

select seq_test.nextval from dual
21

SEQUENCE_NAME NEXTVALUE MIN_VALUE CACHE_SIZE HIGHWATER
--------------- ---------- ---------- ---------- ---------
SEQ_TEST 22 1 20 41


All numbers in cache have missed.