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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 21 |
| 5 | 72 |
| 6 | 229 |
| 7 | 686 |
| 8 | 1972 |
| 9 | 5514 |
| 10 | 15131 |
| 11 | 40986 |
| 12 | 110013 |
| 13 | 293376 |
| 14 | 778678 |
| 15 | 2059646 |
| 16 | 5434009 |
| 17 | 14309508 |
| 18 | 37628165 |
| 19 | 98841306 |
| 20 | 259426800 |
| 21 | 680498610 |
| 22 | 1784183887 |
| 23 | 4676276006 |
| 24 | 12253079101 |
| 25 | 32099813532 |
| 26 | 84080037314 |
| 27 | 220207603686 |
[1,2,6,21,72,229,686,1972,5514,15131,40986,110013, 293376,778678,2059646,5434009,14309508,37628165, 98841306,259426800,680498610,1784183887, 4676276006,12253079101,32099813532,84080037314, 220207603686] |