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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 21 |
| 4 | 74 |
| 5 | 267 |
| 6 | 981 |
| 7 | 3648 |
| 8 | 13690 |
| 9 | 51744 |
| 10 | 196699 |
| 11 | 751237 |
| 12 | 2880345 |
| 13 | 11080081 |
| 14 | 42743148 |
| 15 | 165291569 |
| 16 | 640563158 |
| 17 | 2487083484 |
| 18 | 9672626600 |
| 19 | 37674470433 |
| 20 | 146937686295 |
| 21 | 573781535775 |
| 22 | 2243050091905 |
| 23 | 8777451670102 |
| 24 | 34379401083017 |
| 25 | 134770951530840 |
[1,2,6,21,74,267,981,3648,13690,51744,196699, 751237,2880345,11080081,42743148,165291569, 640563158,2487083484,9672626600,37674470433, 146937686295,573781535775,2243050091905, 8777451670102,34379401083017,134770951530840] |