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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 24 |
| 3 | 96 |
| 4 | 330 |
| 5 | 1104 |
| 6 | 3552 |
| 7 | 11184 |
| 8 | 34584 |
| 9 | 105990 |
| 10 | 322224 |
| 11 | 975264 |
| 12 | 2942016 |
| 13 | 8857680 |
| 14 | 26631312 |
| 15 | 80005632 |
| 16 | 240219114 |
| 17 | 721036320 |
| 18 | 2163789816 |
| 19 | 6492625152 |
| 20 | 19480105392 |
| 21 | 58444390176 |
| 22 | 175340344416 |
| 23 | 526034008752 |
| 24 | 1578124753152 |
| 25 | 4734415061142 |
| 26 | 14203316252400 |
[1,6,24,96,330,1104,3552,11184,34584,105990, 322224,975264,2942016,8857680,26631312,80005632, 240219114,721036320,2163789816,6492625152, 19480105392,58444390176,175340344416,526034008752, 1578124753152,4734415061142,14203316252400] |