How many {followed by} are to/by {Kingdom of Prussia} ?
Kingdom of Prussia is followed by how many?
SELECT (COUNT(?sub) AS ?value ) { ?sub wdt:P156 wd:Q27306 }
SELECT (COUNT(?sub) AS ?subs ) {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> ?sub .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P156> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> http://wikidata.dbpedia.org/resource/Q27306 .
} 

How many followers did the Kingdom of Prussia have?