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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 0 |
| 3 | 2 |
| 4 | 6 |
| 5 | 12 |
| 6 | 34 |
| 7 | 120 |
| 8 | 354 |
| 9 | 1082 |
| 10 | 3636 |
| 11 | 12270 |
| 12 | 40708 |
| 13 | 139062 |
| 14 | 484866 |
| 15 | 1692268 |
| 16 | 5944470 |
| 17 | 21134808 |
| 18 | 75625330 |
| 19 | 271720146 |
| 20 | 982116648 |
| 21 | 3569558058 |
| 22 | 13025614962 |
| 23 | 47714385708 |
| 24 | 175470892468 |
| 25 | 647508620070 |
| 26 | 2396613522804 |
| 27 | 8896422981608 |
| 28 | 33114570409896 |
| 29 | 123566641829256 |
[1,1,0,2,6,12,34,120,354,1082,3636,12270,40708, 139062,484866,1692268,5944470,21134808,75625330, 271720146,982116648,3569558058,13025614962, 47714385708,175470892468,647508620070, 2396613522804,8896422981608,33114570409896, 123566641829256] |