# A048117 (b-file synthesized from sequence entry) 2 1 3 2 4 6 5 18 6 60 7 204 8 720 9 2580 10 9408 11 34668 12 129024 13 483672 14 1824768 15 6919752 16 26357976 17 100778472 18 386591304 19 1487221056 20 5735785176 21 22170562656 22 85866332760 23 333151068528 24 1294658562912 25 5038469947992 26 19634243736168