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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 19 |
| 3 | 75 |
| 4 | 264 |
| 5 | 869 |
| 6 | 2741 |
| 7 | 8396 |
| 8 | 25175 |
| 9 | 74271 |
| 10 | 216336 |
| 11 | 623689 |
| 12 | 1782889 |
| 13 | 5060500 |
| 14 | 14277019 |
| 15 | 40070259 |
| 16 | 111954456 |
| 17 | 311555501 |
| 18 | 863978525 |
| 19 | 2388417116 |
| 20 | 6584117471 |
| 21 | 18104432199 |
| 22 | 49667825184 |
| 23 | 135974484625 |
| 24 | 371543306449 |
| 25 | 1013443026724 |
[1,4,19,75,264,869,2741,8396,25175,74271,216336, 623689,1782889,5060500,14277019,40070259, 111954456,311555501,863978525,2388417116, 6584117471,18104432199,49667825184,135974484625, 371543306449,1013443026724] |