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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 12 |
| 4 | 52 |
| 5 | 240 |
| 6 | 1464 |
| 7 | 10080 |
| 8 | 80736 |
| 9 | 725796 |
| 10 | 7258080 |
| 11 | 79833600 |
| 12 | 958006368 |
| 13 | 12454041600 |
| 14 | 174356602560 |
| 15 | 2615348737440 |
| 16 | 41845579937856 |
| 17 | 711374856192000 |
| 18 | 12804747412916160 |
| 19 | 243290200817664000 |
| 20 | 4865804016367800960 |
| 21 | 102181884343418940480 |
| 22 | 2248001455555375027200 |
[1,4,12,52,240,1464,10080,80736,725796,7258080, 79833600,958006368,12454041600,174356602560, 2615348737440,41845579937856,711374856192000, 12804747412916160,243290200817664000, 4865804016367800960,102181884343418940480, 2248001455555375027200] |