Generate Fibonacci Numbers Using PL/SQL

declare
    f0 integer := 0;
    f1 integer := 1;
    f2 integer := 0;
    i integer := 1;
    upton integer := &upton;
begin
    while (i <= upton) loop
        if (i = 1) then
            dbms_output.put_line(f0);
        elsif (i = 2) then
            dbms_output.put_line(f1);
        else 
            f2 := f0 + f1;
            dbms_output.put_line(f2);
            f0 := f1;
            f1 := f2;
        end if;
        i := i+1;
    end loop;
end;
/

first you should set the server output on. To do so write:
SQL> set serveroutput on;

Enter value for upton: 6
old   6:     upton integer := &upton;
new   6:     upton integer := 6;
0
1
1
2
3
5
PL/SQL procedure successfully completed.