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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 10 |
| 5 | 26 |
| 6 | 276 |
| 7 | 1212 |
| 8 | 4656 |
| 9 | 82224 |
| 10 | 1185120 |
| 11 | 9407520 |
| 12 | 72973440 |
| 13 | 469653120 |
| 14 | 12802164480 |
| 15 | 279210758400 |
| 16 | 5775046502400 |
| 17 | 77253000652800 |
| 18 | 1034866583654400 |
| 19 | 13260091383705600 |
| 20 | 143556727265280000 |
| 21 | 5447593280747520000 |
| 22 | 170937994348154880000 |
[1,1,1,10,26,276,1212,4656,82224,1185120,9407520, 72973440,469653120,12802164480,279210758400, 5775046502400,77253000652800,1034866583654400, 13260091383705600,143556727265280000, 5447593280747520000,170937994348154880000] |