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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 4 |
| 4 | 17 |
| 5 | 60 |
| 6 | 240 |
| 7 | 964 |
| 8 | 4004 |
| 9 | 16900 |
| 10 | 72514 |
| 11 | 315020 |
| 12 | 1383358 |
| 13 | 6129928 |
| 14 | 27376188 |
| 15 | 123094692 |
| 16 | 556796140 |
| 17 | 2531889312 |
| 18 | 11567394600 |
| 19 | 53071061120 |
| 20 | 244417096785 |
| 21 | 1129542027900 |
| 22 | 5236442822520 |
| 23 | 24345395063964 |
| 24 | 113485786553052 |
| 25 | 530298129410920 |
| 26 | 2483549105251580 |
| 27 | 11655428888813128 |
[1,0,2,4,17,60,240,964,4004,16900,72514,315020, 1383358,6129928,27376188,123094692,556796140, 2531889312,11567394600,53071061120,244417096785, 1129542027900,5236442822520,24345395063964, 113485786553052,530298129410920,2483549105251580, 11655428888813128] |