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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 6 |
| 3 | 24 |
| 4 | 80 |
| 5 | 240 |
| 6 | 672 |
| 7 | 1792 |
| 8 | 4608 |
| 9 | 11520 |
| 10 | 28160 |
| 11 | 67584 |
| 12 | 159744 |
| 13 | 372736 |
| 14 | 860160 |
| 15 | 1966080 |
| 16 | 4456448 |
| 17 | 10027008 |
| 18 | 22413312 |
| 19 | 49807360 |
| 20 | 110100480 |
| 21 | 242221056 |
| 22 | 530579456 |
| 23 | 1157627904 |
| 24 | 2516582400 |
| 25 | 5452595200 |
| 26 | 11777605632 |
| 27 | 25367150592 |
| 28 | 54492397568 |
| 29 | 116769423360 |
[0,1,6,24,80,240,672,1792,4608,11520,28160,67584, 159744,372736,860160,1966080,4456448,10027008, 22413312,49807360,110100480,242221056,530579456, 1157627904,2516582400,5452595200,11777605632, 25367150592,54492397568,116769423360] |