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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 3 |
| 4 | 12 |
| 5 | 40 |
| 6 | 163 |
| 7 | 714 |
| 8 | 3426 |
| 9 | 17721 |
| 10 | 98254 |
| 11 | 580316 |
| 12 | 3633281 |
| 13 | 24011156 |
| 14 | 166888166 |
| 15 | 1216070379 |
| 16 | 9264071768 |
| 17 | 73600798036 |
| 18 | 608476008123 |
| 19 | 5224266196934 |
| 20 | 46499892038438 |
| 21 | 428369924118313 |
| 22 | 4078345814329010 |
| 23 | 40073660040755336 |
[1,0,2,3,12,40,163,714,3426,17721,98254,580316, 3633281,24011156,166888166,1216070379,9264071768, 73600798036,608476008123,5224266196934, 46499892038438,428369924118313,4078345814329010, 40073660040755336] |