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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 2 |
| 4 | 8 |
| 5 | 24 |
| 6 | 100 |
| 7 | 488 |
| 8 | 2832 |
| 9 | 19096 |
| 10 | 147296 |
| 11 | 1281392 |
| 12 | 12422864 |
| 13 | 132870368 |
| 14 | 1554525152 |
| 15 | 19750621216 |
| 16 | 270817685568 |
| 17 | 3986140113792 |
| 18 | 62686410981696 |
| 19 | 1048946532137216 |
| 20 | 18608550117641728 |
| 21 | 348854564104019072 |
| 22 | 6891109834644748032 |
| 23 | 143058034748452036352 |
[1,0,2,2,8,24,100,488,2832,19096,147296,1281392, 12422864,132870368,1554525152,19750621216, 270817685568,3986140113792,62686410981696, 1048946532137216,18608550117641728, 348854564104019072,6891109834644748032, 143058034748452036352] |