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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 7 |
| 3 | 40 |
| 4 | 137 |
| 5 | 526 |
| 6 | 1979 |
| 7 | 7092 |
| 8 | 25485 |
| 9 | 90266 |
| 10 | 316415 |
| 11 | 1102336 |
| 12 | 3813841 |
| 13 | 13123366 |
| 14 | 44947139 |
| 15 | 153295692 |
| 16 | 520920213 |
| 17 | 1764401586 |
| 18 | 5958744327 |
| 19 | 20071157144 |
| 20 | 67446281689 |
| 21 | 226154549822 |
| 22 | 756826028235 |
| 23 | 2528141873892 |
| 24 | 8431100881821 |
| 25 | 28073731414730 |
| 26 | 93346571969551 |
| 27 | 309972436014384 |
[1,2,7,40,137,526,1979,7092,25485,90266,316415, 1102336,3813841,13123366,44947139,153295692, 520920213,1764401586,5958744327,20071157144, 67446281689,226154549822,756826028235, 2528141873892,8431100881821,28073731414730, 93346571969551,309972436014384] |