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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 64 |
| 2 | 2144 |
| 3 | 49920 |
| 4 | 905840 |
| 5 | 13627264 |
| 6 | 176638592 |
| 7 | 2025205248 |
| 8 | 20930373880 |
| 9 | 197788352320 |
| 10 | 1728062919232 |
| 11 | 14083242424576 |
| 12 | 107837287452608 |
| 13 | 780481475916160 |
| 14 | 5366307146732800 |
| 15 | 35202669371599360 |
| 16 | 221142159585764508 |
| 17 | 1334633003840266624 |
| 18 | 7760187771579170400 |
[1,64,2144,49920,905840,13627264,176638592, 2025205248,20930373880,197788352320,1728062919232, 14083242424576,107837287452608,780481475916160, 5366307146732800,35202669371599360, 221142159585764508,1334633003840266624, 7760187771579170400] |