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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 2 |
| 5 | 20 |
| 6 | 120 |
| 7 | 570 |
| 8 | 2355 |
| 9 | 8841 |
| 10 | 30906 |
| 11 | 102187 |
| 12 | 323053 |
| 13 | 984354 |
| 14 | 2908671 |
| 15 | 8375521 |
| 16 | 23594410 |
| 17 | 65237027 |
| 18 | 177520325 |
| 19 | 476515378 |
| 20 | 1264297431 |
| 21 | 3321423193 |
| 22 | 8653113914 |
| 23 | 22386784603 |
| 24 | 57586262493 |
| 25 | 147447786562 |
| 26 | 376173191919 |
| 27 | 957113924753 |
| 28 | 2430649701066 |
[0,0,0,0,2,20,120,570,2355,8841,30906,102187, 323053,984354,2908671,8375521,23594410,65237027, 177520325,476515378,1264297431,3321423193, 8653113914,22386784603,57586262493,147447786562, 376173191919,957113924753,2430649701066] |