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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 6 |
| 4 | 24 |
| 5 | 180 |
| 6 | 1080 |
| 7 | 10080 |
| 8 | 90720 |
| 9 | 907200 |
| 10 | 10886400 |
| 11 | 139708800 |
| 12 | 2035756800 |
| 13 | 29578348800 |
| 14 | 479480601600 |
| 15 | 7846046208000 |
| 16 | 146459529216000 |
| 17 | 2845499424768000 |
| 18 | 58421660064768000 |
| 19 | 1246862279190528000 |
| 20 | 28586598596075520000 |
| 21 | 664182248232222720000 |
[1,1,1,6,24,180,1080,10080,90720,907200,10886400, 139708800,2035756800,29578348800,479480601600, 7846046208000,146459529216000,2845499424768000, 58421660064768000,1246862279190528000, 28586598596075520000,664182248232222720000] |