Number of vertices in a planar Apollonian graph at iteration n.

Terms

a(0) =4a(1) =7a(2) =16a(3) =43a(4) =124a(5) =367a(6) =1096a(7) =3283a(8) =9844a(9) =29527a(10) =88576a(11) =265723a(12) =797164a(13) =2391487a(14) =7174456a(15) =21523363a(16) =64570084a(17) =193710247a(18) =581130736a(19) =1743392203a(20) =5230176604a(21) =15690529807a(22) =47071589416a(23) =141214768243a(24) =423644304724