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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 72 |
| 5 | 274 |
| 6 | 1088 |
| 7 | 4462 |
| 8 | 18768 |
| 9 | 80552 |
| 10 | 351452 |
| 11 | 1554360 |
| 12 | 6953182 |
| 13 | 31406472 |
| 14 | 143043384 |
| 15 | 656225618 |
| 16 | 3029606032 |
| 17 | 14065166648 |
| 18 | 65623654844 |
| 19 | 307542991080 |
| 20 | 1447064884324 |
| 21 | 6833469156024 |
| 22 | 32375938380454 |
| 23 | 153853312669856 |
| 24 | 733137984581920 |
| 25 | 3502378475368244 |
| 26 | 16770811951363082 |
| 27 | 80479149475376288 |
[1,2,6,20,72,274,1088,4462,18768,80552,351452, 1554360,6953182,31406472,143043384,656225618, 3029606032,14065166648,65623654844,307542991080, 1447064884324,6833469156024,32375938380454, 153853312669856,733137984581920,3502378475368244, 16770811951363082,80479149475376288] |