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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 3 |
| 2 | 9 |
| 3 | 29 |
| 4 | 80 |
| 5 | 220 |
| 6 | 588 |
| 7 | 1563 |
| 8 | 4125 |
| 9 | 10857 |
| 10 | 28512 |
| 11 | 74792 |
| 12 | 196040 |
| 13 | 513619 |
| 14 | 1345281 |
| 15 | 3522981 |
| 16 | 9224880 |
| 17 | 24153636 |
| 18 | 63239220 |
| 19 | 165569195 |
| 20 | 433476725 |
| 21 | 1134874513 |
| 22 | 2971168704 |
| 23 | 7778667024 |
| 24 | 20364889680 |
| 25 | 53316094755 |
| 26 | 139583544633 |
| 27 | 365434781933 |
[0,3,9,29,80,220,588,1563,4125,10857,28512,74792, 196040,513619,1345281,3522981,9224880,24153636, 63239220,165569195,433476725,1134874513, 2971168704,7778667024,20364889680,53316094755, 139583544633,365434781933] |