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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 40 |
| 3 | 288 |
| 4 | 2184 |
| 5 | 17136 |
| 6 | 137536 |
| 7 | 1121280 |
| 8 | 9244768 |
| 9 | 76866624 |
| 10 | 643311360 |
| 11 | 5412234240 |
| 12 | 45729035520 |
| 13 | 387757278720 |
| 14 | 3297950730240 |
| 15 | 28122838253568 |
| 16 | 240356788028928 |
| 17 | 2058330146595840 |
| 18 | 17657749982408704 |
| 19 | 151716952747917312 |
| 20 | 1305392197618561024 |
| 21 | 11245951765492015104 |
| 22 | 96994770149873909760 |
[1,6,40,288,2184,17136,137536,1121280,9244768, 76866624,643311360,5412234240,45729035520, 387757278720,3297950730240,28122838253568, 240356788028928,2058330146595840, 17657749982408704,151716952747917312, 1305392197618561024,11245951765492015104, 96994770149873909760] |