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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 8 |
| 3 | 40 |
| 4 | 228 |
| 5 | 1404 |
| 6 | 9046 |
| 7 | 59892 |
| 8 | 403486 |
| 9 | 2751104 |
| 10 | 18928024 |
| 11 | 131178640 |
| 12 | 914753916 |
| 13 | 6413644272 |
| 14 | 45188265984 |
| 15 | 319798943360 |
| 16 | 2272481584604 |
| 17 | 16209083200168 |
| 18 | 116019175132958 |
| 19 | 833115842931984 |
| 20 | 6000491719051994 |
| 21 | 43339577695514632 |
| 22 | 313846571416413820 |
[1,2,8,40,228,1404,9046,59892,403486,2751104, 18928024,131178640,914753916,6413644272, 45188265984,319798943360,2272481584604, 16209083200168,116019175132958,833115842931984, 6000491719051994,43339577695514632, 313846571416413820] |