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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 21 |
| 5 | 73 |
| 6 | 240 |
| 7 | 746 |
| 8 | 2217 |
| 9 | 6371 |
| 10 | 17864 |
| 11 | 49202 |
| 12 | 133759 |
| 13 | 360175 |
| 14 | 963044 |
| 15 | 2561604 |
| 16 | 6787167 |
| 17 | 17930815 |
| 18 | 47267250 |
| 19 | 124395032 |
| 20 | 326966211 |
| 21 | 858600521 |
| 22 | 2253029402 |
| 23 | 5908876016 |
| 24 | 15490375561 |
| 25 | 40595804773 |
| 26 | 106364147270 |
| 27 | 278630854386 |
[1,2,6,21,73,240,746,2217,6371,17864,49202,133759, 360175,963044,2561604,6787167,17930815,47267250, 124395032,326966211,858600521,2253029402, 5908876016,15490375561,40595804773,106364147270, 278630854386] |