ADD 5 TO COUNTER IN FOR LOOP

How can I increment  the count in a variable in the loop instead of codeing the actual numbers for the count such as (4,9,14,19,24).  In other words, I just want to add 5 to the counter beginning with record number 4 in the loop.  There can be up to 24  records in the loop.    

This is an oracle table.  I'm using PL/SQL.
See attached code.  

v_count := 0
 
for c1 rec in c1  loop
 v_count := v_count + 1;
 
if v_count in (4,9,14,19,24)  then 
  put_line (l_file,'TEST1');
end if;
 if v_count  in (5,10,15,20) then
  put_line(l_file,TEST2);
end if;
if v_count in (6,11,16,21)
 put_line(l_file,TEST2);
end if;
 
end loop;

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