Number of n-gons with n vertices.

Terms

a(0) =1a(1) =2a(2) =4a(3) =12a(4) =39a(5) =202a(6) =1219a(7) =9468a(8) =83435a(9) =836017a(10) =9223092a(11) =111255228a(12) =1453132944a(13) =20433309147a(14) =307690667072