Number of planar polyhexes (A000228) with at most n cells.

Terms

a(0) =1a(1) =2a(2) =5a(3) =12a(4) =34a(5) =116a(6) =449a(7) =1897a(8) =8469a(9) =38959a(10) =182511a(11) =865612a(12) =4140438a(13) =19937335a(14) =96519210a(15) =469387311a(16) =2291623939a(17) =11226534301a(18) =55165698564a(19) =271816734576