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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 2 |
| 5 | 18 |
| 6 | 99 |
| 7 | 432 |
| 8 | 1641 |
| 9 | 5674 |
| 10 | 18315 |
| 11 | 56076 |
| 12 | 164621 |
| 13 | 466958 |
| 14 | 1287183 |
| 15 | 3463184 |
| 16 | 9125905 |
| 17 | 23617554 |
| 18 | 60162067 |
| 19 | 151126036 |
| 20 | 374931477 |
| 21 | 919863318 |
| 22 | 2234253335 |
| 23 | 5377622040 |
| 24 | 12836667417 |
| 25 | 30410801178 |
| 26 | 71546437659 |
| 27 | 167252066332 |
| 28 | 388677763101 |
| 29 | 898319253534 |
[0,0,0,0,2,18,99,432,1641,5674,18315,56076,164621, 466958,1287183,3463184,9125905,23617554,60162067, 151126036,374931477,919863318,2234253335, 5377622040,12836667417,30410801178,71546437659, 167252066332,388677763101,898319253534] |