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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 28 |
| 5 | 200 |
| 6 | 1926 |
| 7 | 22512 |
| 8 | 306104 |
| 9 | 4770432 |
| 10 | 84234250 |
| 11 | 1663735040 |
| 12 | 36320155092 |
| 13 | 867963393024 |
| 14 | 22535294920334 |
| 15 | 631718010255360 |
| 16 | 19016907901995376 |
| 17 | 611869203759792128 |
| 18 | 20954324710009221138 |
| 19 | 761015341362413371392 |
| 20 | 29214930870257449355660 |
[0,1,2,6,28,200,1926,22512,306104,4770432, 84234250,1663735040,36320155092,867963393024, 22535294920334,631718010255360,19016907901995376, 611869203759792128,20954324710009221138, 761015341362413371392,29214930870257449355660] |