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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 20 |
| 4 | 80 |
| 5 | 384 |
| 6 | 1600 |
| 7 | 7424 |
| 8 | 30720 |
| 9 | 143360 |
| 10 | 593920 |
| 11 | 2703360 |
| 12 | 11403264 |
| 13 | 51118080 |
| 14 | 214958080 |
| 15 | 965738496 |
| 16 | 4047503360 |
| 17 | 17951621120 |
| 18 | 76168560640 |
| 19 | 334202142720 |
| 20 | 1411970498560 |
| 21 | 6211596451840 |
| 22 | 26203595472896 |
| 23 | 114246130073600 |
| 24 | 484815908372480 |
| 25 | 2101441598586880 |
| 26 | 8896148580335616 |
[1,1,4,20,80,384,1600,7424,30720,143360,593920, 2703360,11403264,51118080,214958080,965738496, 4047503360,17951621120,76168560640,334202142720, 1411970498560,6211596451840,26203595472896, 114246130073600,484815908372480,2101441598586880, 8896148580335616] |