Unable to answer "What’s the house number of this building?" – Office Building – https://osm.org/way/166442384 via StreetComplete 57.1:

Haus A

Attached photo(s):
https://westnordost.de/p/201842.jpg
https://westnordost.de/p/201843.jpg
https://westnordost.de/p/201844.jpg