# A001415 (b-file synthesized from sequence entry) 0 1 1 2 2 8 3 60 4 320 5 1980 6 10512 7 60788 8 320896 9 1787904 10 9381840 11 51081844 12 266680992 13 1429703548 14 7432424160 15 39409195740 16 204150606976 17 1073644675448 18 5545305620064