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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 9 |
| 4 | 60 |
| 5 | 545 |
| 6 | 6240 |
| 7 | 86499 |
| 8 | 1407840 |
| 9 | 26328105 |
| 10 | 556338240 |
| 11 | 13110436845 |
| 12 | 340916083200 |
| 13 | 9696978168657 |
| 14 | 299505048041472 |
| 15 | 9982704111951375 |
| 16 | 357144207270359040 |
| 17 | 13651153329833408145 |
| 18 | 555203925284795043840 |
| 19 | 23940076477993593415857 |
| 20 | 1090918710974007336960000 |
| 21 | 52384418915257291697680545 |
[1,1,2,9,60,545,6240,86499,1407840,26328105, 556338240,13110436845,340916083200,9696978168657, 299505048041472,9982704111951375, 357144207270359040,13651153329833408145, 555203925284795043840,23940076477993593415857, 1090918710974007336960000, 52384418915257291697680545] |