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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 12 |
| 5 | 103 |
| 6 | 595 |
| 7 | 6508 |
| 8 | 58800 |
| 9 | 786973 |
| 10 | 9744373 |
| 11 | 155024956 |
| 12 | 2434745852 |
| 13 | 45189575715 |
| 14 | 856361535783 |
| 15 | 18256766891140 |
| 16 | 403804360914560 |
| 17 | 9755015402674937 |
| 18 | 246067759361332137 |
| 19 | 6656604425348335060 |
| 20 | 188304809071878207052 |
| 21 | 5645851709034522319007 |
[0,1,1,4,12,103,595,6508,58800,786973,9744373, 155024956,2434745852,45189575715,856361535783, 18256766891140,403804360914560,9755015402674937, 246067759361332137,6656604425348335060, 188304809071878207052,5645851709034522319007] |