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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 13 |
| 4 | 75 |
| 5 | 541 |
| 6 | 4142 |
| 7 | 34792 |
| 8 | 322904 |
| 9 | 3303160 |
| 10 | 37046948 |
| 11 | 451109712 |
| 12 | 5923255272 |
| 13 | 83424945768 |
| 14 | 1254842021634 |
| 15 | 20081656282038 |
| 16 | 340747127912616 |
| 17 | 6111343349250912 |
| 18 | 115529870445001392 |
| 19 | 2296160998268520576 |
| 20 | 47869541875153872144 |
| 21 | 1044601509263870430000 |
[1,1,3,13,75,541,4142,34792,322904,3303160, 37046948,451109712,5923255272,83424945768, 1254842021634,20081656282038,340747127912616, 6111343349250912,115529870445001392, 2296160998268520576,47869541875153872144, 1044601509263870430000] |