I created a sequence but it isn't run from dual table, where is the problem? [closed]

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//create sequence per_seq start with 1 increment by 1;

select per_seq from dual;
select per_seq from dual
       *
ERROR at line 1:
ORA-00904: "PER_SEQ": invalid identifier

where is problem??,i create sequence but i don't know why it doesn't run.

CREATE SEQUENCE per_seq start with 1 INCREMENT BY 1;
select * from dual;

I create all of this but I don't know where the problem is.