It's about twenty times the number of Keys on a Piano.
It's about one-twenty-fifth the number of Seats in The Colosseum.
In other words, the count of Seats in The Colosseum is 30 times 2,100.(a.k.a. The Coliseum, a.k.a. Flavian Amphitheatre, a.k.a. Amphitheatrum Flavium, a.k.a. Anfiteatro Flavio or Colosseo) (Rome) (estimated)
Built between 70 and 80 AD, The Colosseum was a central attraction of Rome, capable of seating 50,000 spectators for various events including plays, war reenactments, and gladiatorial matches. The structure was estimated to require 100,000 cu. m of stone to construct. It remains the largest amphitheater in the world.
It's about thirty times the number of Submarines in the US Navy.
It's about one-fortieth the number of Seats in Lambeau Field.
In other words, 2,100 is 0.026011 times the count of Seats in Lambeau Field, and the count of Seats in Lambeau Field is 38.445 times that amount.(2014 figures) (a.k.a. City Stadium, a.k.a. New City Stadium, a.k.a. Titletown USA, a.k.a. The Frozen Tundra, a.k.a. The Shrine of Pro Football) (Green Bay, Wisconsin)
It's about forty times the number of Countries in Africa.
In other words, the count of Countries in Africa is 0.026 times 2,100.(2016 figures) (sovereign states recognized by the UN only)
It's about 45 times the number of Teeth in a Great White Shark's Mouth.
In other words, the count of Teeth in a Great White Shark's Mouth is 0.023 times 2,100.(Carcharodon carcharias) (average; including developing rows)
It's about 75 times the number of Countries in the European Union.
In other words, the count of Countries in the European Union is 0.013 times 2,100.(a.k.a. EU) (2016 figures)