# A026899 (b-file synthesized from sequence entry) 1 1 2 6 3 30 4 144 5 687 6 3296 7 15972 8 78294 9 388320 10 1947910 11 9875566 12 50560246 13 261177401 14 1360112590 15 7134802722 16 37673830960 17 200106632766 18 1068539351340 19 5733226876876 20 30894846668416 21 167137498306038 22 907416216735816