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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 4 |
| 4 | 12 |
| 5 | 40 |
| 6 | 154 |
| 7 | 656 |
| 8 | 3074 |
| 9 | 15615 |
| 10 | 85314 |
| 11 | 497262 |
| 12 | 3068890 |
| 13 | 19899645 |
| 14 | 134520386 |
| 15 | 940841796 |
| 16 | 6760952170 |
| 17 | 49617422739 |
| 18 | 370013347266 |
| 19 | 2792665457338 |
| 20 | 21266237427018 |
| 21 | 163008076378489 |
| 22 | 1255477313622210 |
| 23 | 9703388630792784 |
[1,2,4,12,40,154,656,3074,15615,85314,497262, 3068890,19899645,134520386,940841796,6760952170, 49617422739,370013347266,2792665457338, 21266237427018,163008076378489,1255477313622210, 9703388630792784] |