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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 2 |
| 4 | 16 |
| 5 | 84 |
| 6 | 408 |
| 7 | 1926 |
| 8 | 8776 |
| 9 | 38912 |
| 10 | 169456 |
| 11 | 727914 |
| 12 | 3091712 |
| 13 | 13010668 |
| 14 | 54334792 |
| 15 | 225449486 |
| 16 | 930278584 |
| 17 | 3820249240 |
| 18 | 15622389664 |
| 19 | 63649588850 |
| 20 | 258473068912 |
| 21 | 1046543827972 |
| 22 | 4226200851704 |
| 23 | 17025631341974 |
| 24 | 68440231400232 |
[0,0,2,16,84,408,1926,8776,38912,169456,727914, 3091712,13010668,54334792,225449486,930278584, 3820249240,15622389664,63649588850,258473068912, 1046543827972,4226200851704,17025631341974, 68440231400232] |