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| n | a(n) |
|---|---|
| 2 | 1 |
| 3 | 2 |
| 4 | 7 |
| 5 | 18 |
| 6 | 56 |
| 7 | 168 |
| 8 | 543 |
| 9 | 1792 |
| 10 | 6187 |
| 11 | 22088 |
| 12 | 81766 |
| 13 | 313224 |
| 14 | 1239764 |
| 15 | 5068320 |
| 16 | 21355894 |
| 17 | 92714368 |
| 18 | 413918310 |
| 19 | 1899260064 |
| 20 | 8941942444 |
| 21 | 43168351136 |
| 22 | 213385362136 |
| 23 | 1079240048256 |
| 24 | 5578228510556 |
| 25 | 29443746273792 |
| 26 | 158547033453372 |
| 27 | 870370433845888 |
| 28 | 4866859876496872 |
[1,2,7,18,56,168,543,1792,6187,22088,81766,313224, 1239764,5068320,21355894,92714368,413918310, 1899260064,8941942444,43168351136,213385362136, 1079240048256,5578228510556,29443746273792, 158547033453372,870370433845888,4866859876496872] |