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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 12 |
| 4 | 57 |
| 5 | 305 |
| 6 | 1787 |
| 7 | 11269 |
| 8 | 75629 |
| 9 | 535960 |
| 10 | 3987913 |
| 11 | 31021693 |
| 12 | 251445581 |
| 13 | 2117993712 |
| 14 | 18499513147 |
| 15 | 167246537937 |
| 16 | 1562556275281 |
| 17 | 15066167302802 |
| 18 | 149737897716757 |
| 19 | 1532313152898208 |
| 20 | 16129331500727047 |
[1,1,3,12,57,305,1787,11269,75629,535960,3987913, 31021693,251445581,2117993712,18499513147, 167246537937,1562556275281,15066167302802, 149737897716757,1532313152898208, 16129331500727047] |