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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 2 |
| 4 | 7 |
| 5 | 22 |
| 6 | 68 |
| 7 | 198 |
| 8 | 563 |
| 9 | 1578 |
| 10 | 4367 |
| 11 | 11980 |
| 12 | 32648 |
| 13 | 88500 |
| 14 | 238886 |
| 15 | 642598 |
| 16 | 1723629 |
| 17 | 4612170 |
| 18 | 12316357 |
| 19 | 32832302 |
| 20 | 87390763 |
| 21 | 232305470 |
| 22 | 616812557 |
| 23 | 1636084020 |
| 24 | 4335770052 |
| 25 | 11480937084 |
| 26 | 30379110906 |
| 27 | 80332372838 |
| 28 | 212300488377 |
[0,0,0,2,7,22,68,198,563,1578,4367,11980,32648, 88500,238886,642598,1723629,4612170,12316357, 32832302,87390763,232305470,616812557,1636084020, 4335770052,11480937084,30379110906,80332372838, 212300488377] |