with a as

(
select  54 totcnt from dual
)
select 20*(level-1)+1,
       case when (20*(level) < totcnt ) then 20*(level)
            else totcnt  
       end case,
       case when (20*(level) < totcnt ) then 20
            else 54 - 20*(level-1) 
       end case      
from a
connect by level <=  round(totcnt/20);

SELECT (LEVEL - 1) * 20 + 1 stacnt
     , LEAST(LEVEL * 20, totcnt) endcnt
     , LEAST(LEVEL * 20, totcnt) - (LEVEL - 1) * 20 cnt
  FROM (SELECT 54 totcnt FROM dual)
 CONNECT BY LEVEL <= CEIL(totcnt / 20)
;