Whitney number of level n of the lattice of the ideals of the fence of order 2 n + 1.

Terms

a(0) =1a(1) =2a(2) =3a(3) =7a(4) =17a(5) =40a(6) =97a(7) =238a(8) =587a(9) =1458a(10) =3640a(11) =9124a(12) =22951a(13) =57904a(14) =146461a(15) =371281a(16) =943045a(17) =2399460a(18) =6114555a(19) =15603339a(20) =39866932a(21) =101976512a(22) =261117378a(23) =669239402a(24) =1716737267a(25) =4407306170a(26) =11323050897a(27) =29110603423a(28) =74888578067