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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 120 |
| 6 | 694 |
| 7 | 4676 |
| 8 | 35952 |
| 9 | 310464 |
| 10 | 2984176 |
| 11 | 31536583 |
| 12 | 363591384 |
| 13 | 4541789148 |
| 14 | 61089594448 |
| 15 | 880428095803 |
| 16 | 13534614549829 |
| 17 | 221066397540186 |
| 18 | 3823205871530350 |
| 19 | 69792946997645295 |
| 20 | 1341134146478847104 |
| 21 | 27059669661295560098 |
| 22 | 571973335506443017436 |
[1,1,2,6,24,120,694,4676,35952,310464,2984176, 31536583,363591384,4541789148,61089594448, 880428095803,13534614549829,221066397540186, 3823205871530350,69792946997645295, 1341134146478847104,27059669661295560098, 571973335506443017436] |