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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 27 |
| 4 | 256 |
| 5 | 3152 |
| 6 | 47680 |
| 7 | 854802 |
| 8 | 17711872 |
| 9 | 416372620 |
| 10 | 10947581056 |
| 11 | 318304921165 |
| 12 | 10140097538560 |
| 13 | 351219420860694 |
| 14 | 13141237470041536 |
| 15 | 528208859187285899 |
| 16 | 22698715714385041920 |
| 17 | 1038485165851106374784 |
| 18 | 50395972495225521776384 |
| 19 | 2585595617532863164095240 |
| 20 | 139835798146777767415142912 |
| 21 | 7950987913261988583226011167 |
[1,1,4,27,256,3152,47680,854802,17711872, 416372620,10947581056,318304921165,10140097538560, 351219420860694,13141237470041536, 528208859187285899,22698715714385041920, 1038485165851106374784,50395972495225521776384, 2585595617532863164095240, 139835798146777767415142912, 7950987913261988583226011167] |