A recent paper published in Nature Human Behaviour adds a new number to social relationships. It is to do with place and is called location capacity.
Relationships with people
5 Support Clique: those that would actively help you in a crisis.
15 Sympathy Group: those that would be genuinely sympathetic in a crisis.
50 Actively Engaged Groups — size of communities with everyone regularly contributing Source
150 Dunbar Number: “the number of people you would not feel embarrassed about joining uninvited for a drink if you happened to bump into them in a bar”
Circles of acquaintanceship, scale relative to each other by a factor of three (an inner core of five intimates, and then successive layers at 15, 50 and 150).
Relationships with places and things
9 Apps. 9 apps daily, 30 monthly. Source (unlike the other numbers there is a lot of data to suggest this number may have something to do with attention capacity, but it is from one type of relationship so isn’t corroborated).
25 Location Capacity (number of familiar locations an individual visits at any point) Source