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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 20 |
| 5 | 68 |
| 6 | 233 |
| 7 | 805 |
| 8 | 2807 |
| 9 | 9879 |
| 10 | 35073 |
| 11 | 125513 |
| 12 | 452389 |
| 13 | 1641029 |
| 14 | 5986994 |
| 15 | 21954974 |
| 16 | 80884424 |
| 17 | 299233544 |
| 18 | 1111219334 |
| 19 | 4140813374 |
| 20 | 15478839554 |
| 21 | 58028869154 |
| 22 | 218123355524 |
| 23 | 821908275548 |
| 24 | 3104046382352 |
| 25 | 11747506651600 |
| 26 | 44546351423300 |
| 27 | 169227201341652 |
[1,1,2,6,20,68,233,805,2807,9879,35073,125513, 452389,1641029,5986994,21954974,80884424, 299233544,1111219334,4140813374,15478839554, 58028869154,218123355524,821908275548, 3104046382352,11747506651600,44546351423300, 169227201341652] |