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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 72 |
| 3 | 1200 |
| 4 | 19600 |
| 5 | 635040 |
| 6 | 25613280 |
| 7 | 82450368 |
| 8 | 9275666400 |
| 9 | 595703908800 |
| 10 | 2048086772160 |
| 11 | 23459903026560 |
| 12 | 413676290035008 |
| 13 | 4419618483280000 |
| 14 | 3221901874311120000 |
| 15 | 361282596839420256000 |
| 16 | 2630246784565779288000 |
| 17 | 9628029406360113091200 |
| 18 | 1310481780310126504080000 |
[1,4,72,1200,19600,635040,25613280,82450368, 9275666400,595703908800,2048086772160, 23459903026560,413676290035008,4419618483280000, 3221901874311120000,361282596839420256000, 2630246784565779288000,9628029406360113091200, 1310481780310126504080000] |