sql recursion

WITH miCTE AS (
   
     SELECT MIN(idcaf_activo) as n,(select max(idcaf_activo) from caf_activos) as maxid from caf_activos
     UNION all
     SELECT n+1,maxid from miCTE where n < maxid
)
SELECT n FROM miCTE  t1 left join (select * from caf_activos)t2 on t2.idcaf_activo=t1.n
where t2.idcaf_activo is null
OPTION (MAXRECURSION 0)

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