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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 6 |
| 4 | 40 |
| 5 | 198 |
| 6 | 910 |
| 7 | 3848 |
| 8 | 15492 |
| 9 | 59920 |
| 10 | 224917 |
| 11 | 824074 |
| 12 | 2960828 |
| 13 | 10466610 |
| 14 | 36498195 |
| 15 | 125801144 |
| 16 | 429284612 |
| 17 | 1452174984 |
| 18 | 4874940295 |
| 19 | 16254780970 |
| 20 | 53873727516 |
| 21 | 177594715034 |
| 22 | 582603630260 |
| 23 | 1902860189328 |
| 24 | 6190199896600 |
| 25 | 20064013907288 |
| 26 | 64815504118695 |
| 27 | 208739559416878 |
| 28 | 670345766842528 |
[0,1,6,40,198,910,3848,15492,59920,224917,824074, 2960828,10466610,36498195,125801144,429284612, 1452174984,4874940295,16254780970,53873727516, 177594715034,582603630260,1902860189328, 6190199896600,20064013907288,64815504118695, 208739559416878,670345766842528] |