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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 24 |
| 5 | 180 |
| 6 | 900 |
| 7 | 3780 |
| 8 | 175728 |
| 9 | 4951044 |
| 10 | 86365500 |
| 11 | 1153213380 |
| 12 | 23556955752 |
| 13 | 859608051588 |
| 14 | 28980467230260 |
| 15 | 782915612415300 |
| 16 | 20550183180508896 |
| 17 | 708162598061362692 |
| 18 | 30250472697427079340 |
| 19 | 1248019079468428688580 |
| 20 | 47622250712947210524120 |
| 21 | 1899094232159722382052996 |
[1,0,0,0,24,180,900,3780,175728,4951044,86365500, 1153213380,23556955752,859608051588, 28980467230260,782915612415300,20550183180508896, 708162598061362692,30250472697427079340, 1248019079468428688580,47622250712947210524120, 1899094232159722382052996] |