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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 4 |
| 3 | 14 |
| 4 | 54 |
| 5 | 292 |
| 6 | 1696 |
| 7 | 12500 |
| 8 | 97300 |
| 9 | 909800 |
| 10 | 8888400 |
| 11 | 100778200 |
| 12 | 1185163000 |
| 13 | 15798002000 |
| 14 | 217275712000 |
| 15 | 3329482106000 |
| 16 | 52433793018000 |
| 17 | 908110694260000 |
| 18 | 16113910669480000 |
| 19 | 311249886303980000 |
| 20 | 6144485548655740000 |
[1,2,4,14,54,292,1696,12500,97300,909800,8888400, 100778200,1185163000,15798002000,217275712000, 3329482106000,52433793018000,908110694260000, 16113910669480000,311249886303980000, 6144485548655740000] |