# A009224 (b-file synthesized from sequence entry) 0 0 1 1 2 2 3 3 4 8 5 25 6 72 7 259 8 1024 9 4113 10 18720 11 89859 12 451200 13 2452905 14 13870976 15 82466115 16 517341184 17 3364642465 18 22907884032 19 162289204995 20 1190546278400 21 9080010901689 22 71557772290048 23 582825476943747 24 4904509780131840