query: SELECT ?item ?catcode ?catnum ?catletter WHERE { 
  ?item p:P528 [ pq:P972 wd:Q106625435 ; ps:P528 ?catcode].  
  BIND( xsd:decimal(REPLACE(?catcode, "[a-zA-Z().-]", "")) AS ?catnum) 
  BIND(REPLACE(?catcode, "[0-9]*", "") AS ?catletter) 
  } ORDER BY ?catnum ?catletter