query: SELECT ?item ?catcode  ?catnum ?catletter WHERE { 
  ?item p:P528 [ pq:P972 wd:Q106508006 ; ps:P528 ?catcode].  
  BIND( xsd:integer(REPLACE(?catcode, "[a-zA-Z]", "")) AS ?catnum) .
  BIND(REPLACE(?catcode, "[0-9]*", "") AS ?catletter) .
  } ORDER BY ?catnum ?catletter