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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 6 |
| 3 | 90 |
| 4 | 2520 |
| 5 | 113400 |
| 6 | 3356640 |
| 7 | 75336660 |
| 8 | 1500131820 |
| 9 | 29660400822 |
| 10 | 620330067782 |
| 11 | 13125403608162 |
| 12 | 274194614811528 |
| 13 | 5605288189594200 |
| 14 | 112437639146871360 |
| 15 | 2235073249396108440 |
| 16 | 44209749453949113840 |
| 17 | 870798759948756386976 |
| 18 | 17069437222534487122608 |
| 19 | 332789644153015982087550 |
| 20 | 6455422726721469064982952 |
[1,1,6,90,2520,113400,3356640,75336660,1500131820, 29660400822,620330067782,13125403608162, 274194614811528,5605288189594200, 112437639146871360,2235073249396108440, 44209749453949113840,870798759948756386976, 17069437222534487122608,332789644153015982087550, 6455422726721469064982952] |