Number of 10 up, 10 down permutations of [n].

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =1a(6) =1a(7) =1a(8) =1a(9) =1a(10) =1a(11) =1a(12) =11a(13) =66a(14) =286a(15) =1001a(16) =3003a(17) =8008a(18) =19448a(19) =43758a(20) =92378a(21) =184756a(22) =3711916a(23) =39277446a(24) =290971966a(25) =1693270006a(26) =8237327526a(27) =34822561201a(28) =131333661601a(29) =450356465701