Number of 5 up, 5 down permutations of [n].

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =1a(6) =1a(7) =6a(8) =21a(9) =56a(10) =126a(11) =252a(12) =2562a(13) =14442a(14) =59487a(15) =199627a(16) =578005a(17) =8330800a(18) =65056960a(19) =363823800a(20) =1628423880a(21) =6190034016a(22) =115452938151