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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 1 |
| 3 | 1 |
| 4 | 4 |
| 5 | 9 |
| 6 | 31 |
| 7 | 94 |
| 8 | 337 |
| 9 | 1185 |
| 10 | 4540 |
| 11 | 17581 |
| 12 | 71875 |
| 13 | 299646 |
| 14 | 1299637 |
| 15 | 5760973 |
| 16 | 26357764 |
| 17 | 123241185 |
| 18 | 591877543 |
| 19 | 2902472734 |
| 20 | 14571525145 |
| 21 | 74613410169 |
| 22 | 390197960716 |
| 23 | 2078859419077 |
| 24 | 11290463266843 |
| 25 | 62400316038462 |
| 26 | 351037047533581 |
| 27 | 2007507147853429 |
[1,0,1,1,4,9,31,94,337,1185,4540,17581,71875, 299646,1299637,5760973,26357764,123241185, 591877543,2902472734,14571525145,74613410169, 390197960716,2078859419077,11290463266843, 62400316038462,351037047533581,2007507147853429] |