Number of polyhedral orientations with n inner vertices.

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =0a(5) =3a(6) =4a(7) =15a(8) =39a(9) =122a(10) =375a(11) =1212a(12) =3980a(13) =13413a(14) =45966a(15) =160295a(16) =566985a(17) =2032110a(18) =7368334a(19) =27000759a(20) =99891654a(21) =372788553a(22) =1402339329a(23) =5313959388a(24) =20272563265a(25) =77822173758a(26) =300473023929