query: SELECT ?cat 
  
  WITH { 
    SELECT ?cat WHERE {
        ?cat wdt:P31 wd:Q4167836 
    } OFFSET 2000000 LIMIT 500000
  } AS %cats
  
  WHERE {
      INCLUDE %cats .
      OPTIONAL {?cat p:P971/pq:P3831 ?value} .
      FILTER (!bound(?value))
  }
                           