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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 10 |
| 5 | 70 |
| 6 | 630 |
| 7 | 6930 |
| 8 | 90090 |
| 9 | 90090 |
| 10 | 1531530 |
| 11 | 29099070 |
| 12 | 29099070 |
| 13 | 669278610 |
| 14 | 3346393050 |
| 15 | 10039179150 |
| 16 | 291136195350 |
| 17 | 9025222055850 |
| 18 | 9025222055850 |
| 19 | 9025222055850 |
| 20 | 333933216066450 |
[1,1,1,2,10,70,630,6930,90090,90090,1531530, 29099070,29099070,669278610,3346393050, 10039179150,291136195350,9025222055850, 9025222055850,9025222055850,333933216066450] |