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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 14 |
| 5 | 90 |
| 6 | 738 |
| 7 | 7364 |
| 8 | 86608 |
| 9 | 1173240 |
| 10 | 17990600 |
| 11 | 308055528 |
| 12 | 5826331440 |
| 13 | 120629547584 |
| 14 | 2713659864832 |
| 15 | 65909241461760 |
| 16 | 1718947213795328 |
| 17 | 47912968352783232 |
| 18 | 1421417290991105664 |
| 19 | 44717945211445216640 |
| 20 | 1487040748881346835200 |
| 21 | 52117255681017313721088 |
[0,1,1,3,14,90,738,7364,86608,1173240,17990600, 308055528,5826331440,120629547584,2713659864832, 65909241461760,1718947213795328,47912968352783232, 1421417290991105664,44717945211445216640, 1487040748881346835200,52117255681017313721088] |