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

Terms

a(0) =1a(1) =1a(2) =2a(3) =5a(4) =11a(5) =26a(6) =63a(7) =153a(8) =376a(9) =931a(10) =2317a(11) =5794a(12) =14545a(13) =36631a(14) =92512a(15) =234205a(16) =594169a(17) =1510192a(18) =3844787a(19) =9802895a(20) =25027296a(21) =63972861a(22) =163701327a(23) =419316330a(24) =1075049011a(25) =2758543201a(26) =7083830648a(27) =18204064403a(28) =46812088751a(29) =120452857976