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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 13 |
| 4 | 73 |
| 5 | 501 |
| 6 | 4050 |
| 7 | 37632 |
| 8 | 394296 |
| 9 | 4595976 |
| 10 | 58932720 |
| 11 | 823949280 |
| 12 | 12467513520 |
| 13 | 202933851120 |
| 14 | 3534322952160 |
| 15 | 65559527953920 |
| 16 | 1290129736896000 |
| 17 | 26840074522060800 |
| 18 | 588476031700677120 |
| 19 | 13560642403296468480 |
| 20 | 327603687047488051200 |
| 21 | 8278733693718654566400 |
[1,1,3,13,73,501,4050,37632,394296,4595976, 58932720,823949280,12467513520,202933851120, 3534322952160,65559527953920,1290129736896000, 26840074522060800,588476031700677120, 13560642403296468480,327603687047488051200, 8278733693718654566400] |