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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 48 |
| 3 | 312 |
| 4 | 2064 |
| 5 | 12768 |
| 6 | 79680 |
| 7 | 484224 |
| 8 | 2947584 |
| 9 | 17783808 |
| 10 | 107268096 |
| 11 | 644960256 |
| 12 | 3877367808 |
| 13 | 23282294784 |
| 14 | 139790696448 |
| 15 | 838984925184 |
| 16 | 5035133042688 |
| 17 | 30213857476608 |
| 18 | 181298502303744 |
| 19 | 1087829443608576 |
| 20 | 6527166069080064 |
| 21 | 39163476131708928 |
| 22 | 234983177934864384 |
[1,6,48,312,2064,12768,79680,484224,2947584, 17783808,107268096,644960256,3877367808, 23282294784,139790696448,838984925184, 5035133042688,30213857476608,181298502303744, 1087829443608576,6527166069080064, 39163476131708928,234983177934864384] |