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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 9 |
| 4 | 56 |
| 5 | 360 |
| 6 | 2934 |
| 7 | 26054 |
| 8 | 269128 |
| 9 | 3010680 |
| 10 | 37616880 |
| 11 | 504880992 |
| 12 | 7387701672 |
| 13 | 115228447152 |
| 14 | 1929016301016 |
| 15 | 34194883090440 |
| 16 | 643667407174464 |
| 17 | 12757366498618176 |
| 18 | 266426229010029696 |
| 19 | 5830527979298793024 |
| 20 | 133665090871032478080 |
| 21 | 3197905600674249843840 |
[1,1,2,9,56,360,2934,26054,269128,3010680, 37616880,504880992,7387701672,115228447152, 1929016301016,34194883090440,643667407174464, 12757366498618176,266426229010029696, 5830527979298793024,133665090871032478080, 3197905600674249843840] |