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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 3 |
| 3 | 8 |
| 4 | 33 |
| 5 | 120 |
| 6 | 451 |
| 7 | 1680 |
| 8 | 6273 |
| 9 | 23408 |
| 10 | 87363 |
| 11 | 326040 |
| 12 | 1216801 |
| 13 | 4541160 |
| 14 | 16947843 |
| 15 | 63250208 |
| 16 | 236052993 |
| 17 | 880961760 |
| 18 | 3287794051 |
| 19 | 12270214440 |
| 20 | 45793063713 |
| 21 | 170902040408 |
| 22 | 637815097923 |
| 23 | 2380358351280 |
| 24 | 8883618307201 |
[1,0,3,8,33,120,451,1680,6273,23408,87363,326040, 1216801,4541160,16947843,63250208,236052993, 880961760,3287794051,12270214440,45793063713, 170902040408,637815097923,2380358351280, 8883618307201] |