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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 28 |
| 4 | 304 |
| 5 | 2976 |
| 6 | 27488 |
| 7 | 244544 |
| 8 | 2119168 |
| 9 | 18011136 |
| 10 | 150809088 |
| 11 | 1247857664 |
| 12 | 10226274304 |
| 13 | 83138240512 |
| 14 | 671370043392 |
| 15 | 5390483210240 |
| 16 | 43066315243520 |
| 17 | 342583723687936 |
| 18 | 2714813886234624 |
| 19 | 21440990518444032 |
| 20 | 168825545758343168 |
[0,2,28,304,2976,27488,244544,2119168,18011136, 150809088,1247857664,10226274304,83138240512, 671370043392,5390483210240,43066315243520, 342583723687936,2714813886234624, 21440990518444032,168825545758343168] |