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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 20 |
| 3 | 276 |
| 4 | 4544 |
| 5 | 84496 |
| 6 | 1723960 |
| 7 | 37906608 |
| 8 | 887437120 |
| 9 | 21930970336 |
| 10 | 568496401152 |
| 11 | 15384167213056 |
| 12 | 433012038646112 |
| 13 | 12640210696664768 |
| 14 | 381804410640552576 |
| 15 | 11911194405763099520 |
| 16 | 383211218811649633792 |
| 17 | 12698182733530048241152 |
[1,2,20,276,4544,84496,1723960,37906608,887437120, 21930970336,568496401152,15384167213056, 433012038646112,12640210696664768, 381804410640552576,11911194405763099520, 383211218811649633792,12698182733530048241152] |