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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 12 |
| 3 | 56 |
| 4 | 280 |
| 5 | 1440 |
| 6 | 7488 |
| 7 | 39104 |
| 8 | 204544 |
| 9 | 1070592 |
| 10 | 5604864 |
| 11 | 29345792 |
| 12 | 153653248 |
| 13 | 804532224 |
| 14 | 4212572160 |
| 15 | 22057287680 |
| 16 | 115493404672 |
| 17 | 604731211776 |
| 18 | 3166413520896 |
| 19 | 16579556016128 |
| 20 | 86811681488896 |
| 21 | 454551863820288 |
[1,3,12,56,280,1440,7488,39104,204544,1070592, 5604864,29345792,153653248,804532224,4212572160, 22057287680,115493404672,604731211776, 3166413520896,16579556016128,86811681488896, 454551863820288] |