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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 1 |
| 3 | 3 |
| 4 | 15 |
| 5 | 90 |
| 6 | 645 |
| 7 | 5355 |
| 8 | 50505 |
| 9 | 532980 |
| 10 | 6219045 |
| 11 | 79469775 |
| 12 | 1103335695 |
| 13 | 16533226710 |
| 14 | 265888247625 |
| 15 | 4566885297975 |
| 16 | 83422361847825 |
| 17 | 1614626682669000 |
| 18 | 33003508539026025 |
| 19 | 710350201433547675 |
| 20 | 16057073233633006575 |
[1,0,1,3,15,90,645,5355,50505,532980,6219045, 79469775,1103335695,16533226710,265888247625, 4566885297975,83422361847825,1614626682669000, 33003508539026025,710350201433547675, 16057073233633006575] |