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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 80 |
| 6 | 240 |
| 7 | 896 |
| 8 | 3584 |
| 9 | 15360 |
| 10 | 65792 |
| 11 | 270336 |
| 12 | 1081344 |
| 13 | 4259840 |
| 14 | 16773120 |
| 15 | 66584576 |
| 16 | 266338304 |
| 17 | 1069547520 |
| 18 | 4295032832 |
| 19 | 17213423616 |
| 20 | 68853694464 |
| 21 | 275146342400 |
| 22 | 1099510579200 |
| 23 | 4395899027456 |
| 24 | 17583596109824 |
| 25 | 70351564308480 |
| 26 | 281474993487872 |
[0,2,6,24,80,240,896,3584,15360,65792,270336, 1081344,4259840,16773120,66584576,266338304, 1069547520,4295032832,17213423616,68853694464, 275146342400,1099510579200,4395899027456, 17583596109824,70351564308480,281474993487872] |