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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 64 |
| 2 | 1984 |
| 3 | 39680 |
| 4 | 575424 |
| 5 | 6448000 |
| 6 | 58115328 |
| 7 | 433131008 |
| 8 | 2724906944 |
| 9 | 14709082432 |
| 10 | 69079796864 |
| 11 | 285848172800 |
| 12 | 1054968628480 |
| 13 | 3515371815296 |
| 14 | 10706472186368 |
| 15 | 30156949879296 |
| 16 | 79395777333184 |
| 17 | 197101549419648 |
| 18 | 464573878394560 |
| 19 | 1045365667116800 |
| 20 | 2256126097001600 |
| 21 | 4689805691447296 |
[1,64,1984,39680,575424,6448000,58115328, 433131008,2724906944,14709082432,69079796864, 285848172800,1054968628480,3515371815296, 10706472186368,30156949879296,79395777333184, 197101549419648,464573878394560,1045365667116800, 2256126097001600,4689805691447296] |