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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 6 |
| 3 | 75 |
| 4 | 1416 |
| 5 | 36100 |
| 6 | 1162500 |
| 7 | 45298260 |
| 8 | 2073120000 |
| 9 | 109025236656 |
| 10 | 6479480327040 |
| 11 | 429490443634560 |
| 12 | 31416341604500160 |
| 13 | 2513890936457746560 |
| 14 | 218444719852713594240 |
| 15 | 20484930511629760176000 |
| 16 | 2062040084613184977100800 |
| 17 | 221771483779991107676313600 |
| 18 | 25379627910164829624284881920 |
[1,1,6,75,1416,36100,1162500,45298260,2073120000, 109025236656,6479480327040,429490443634560, 31416341604500160,2513890936457746560, 218444719852713594240,20484930511629760176000, 2062040084613184977100800, 221771483779991107676313600, 25379627910164829624284881920] |