query: SELECT ?item ?catcode WHERE { 
      ?item p:P528 [ pq:P972 wd:Q17280421 ; ps:P528 ?catcode].  
      BIND( xsd:integer(REPLACE(?catcode, "[a-zA-Z]", "")) AS ?catnum)
      BIND(REPLACE(?catcode, "F[0-9]*", "") AS ?catletter)
    }
  ORDER BY ?catnum ?catletter