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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 2 |
| 5 | 12 |
| 6 | 60 |
| 7 | 408 |
| 8 | 2640 |
| 9 | 24480 |
| 10 | 208080 |
| 11 | 2262960 |
| 12 | 23950080 |
| 13 | 307359360 |
| 14 | 3835641600 |
| 15 | 57400358400 |
| 16 | 825160089600 |
| 17 | 13909727462400 |
| 18 | 229664981145600 |
| 19 | 4310966499840000 |
| 20 | 79428141112320000 |
| 21 | 1658163790483200000 |
| 22 | 33795850208440320000 |
| 23 | 770528520983789568000 |
[1,0,0,1,2,12,60,408,2640,24480,208080,2262960, 23950080,307359360,3835641600,57400358400, 825160089600,13909727462400,229664981145600, 4310966499840000,79428141112320000, 1658163790483200000,33795850208440320000, 770528520983789568000] |