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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 3 |
| 3 | 0 |
| 4 | 2 |
| 5 | 6 |
| 6 | 13 |
| 7 | 22 |
| 8 | 68 |
| 9 | 132 |
| 10 | 323 |
| 11 | 790 |
| 12 | 1724 |
| 13 | 4158 |
| 14 | 10007 |
| 15 | 22770 |
| 16 | 54346 |
| 17 | 129582 |
| 18 | 301431 |
| 19 | 715256 |
| 20 | 1697866 |
| 21 | 3987490 |
| 22 | 9441255 |
| 23 | 22363356 |
| 24 | 52732570 |
| 25 | 124755460 |
| 26 | 295222595 |
| 27 | 697290424 |
| 28 | 1649165304 |
| 29 | 3900971604 |
| 30 | 9220090253 |
| 31 | 21804026010 |
[0,3,0,2,6,13,22,68,132,323,790,1724,4158,10007, 22770,54346,129582,301431,715256,1697866,3987490, 9441255,22363356,52732570,124755460,295222595, 697290424,1649165304,3900971604,9220090253, 21804026010] |