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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 0 |
| 3 | 0 |
| 4 | 3 |
| 5 | 5 |
| 6 | 12 |
| 7 | 54 |
| 8 | 426 |
| 9 | 2334 |
| 10 | 23280 |
| 11 | 152820 |
| 12 | 1939740 |
| 13 | 14564760 |
| 14 | 222925920 |
| 15 | 1890254100 |
| 16 | 33899743010 |
| 17 | 320743643010 |
| 18 | 6597891367200 |
| 19 | 68944295861280 |
| 20 | 1600434039456630 |
| 21 | 18309730315533930 |
| 22 | 473501454337711800 |
[1,0,0,3,5,12,54,426,2334,23280,152820,1939740, 14564760,222925920,1890254100,33899743010, 320743643010,6597891367200,68944295861280, 1600434039456630,18309730315533930, 473501454337711800] |