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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 1 |
| 5 | 2 |
| 6 | 4 |
| 7 | 11 |
| 8 | 20 |
| 9 | 40 |
| 10 | 109 |
| 11 | 198 |
| 12 | 396 |
| 13 | 1079 |
| 14 | 1960 |
| 15 | 3920 |
| 16 | 10681 |
| 17 | 19402 |
| 18 | 38804 |
| 19 | 105731 |
| 20 | 192060 |
| 21 | 384120 |
| 22 | 1046629 |
| 23 | 1901198 |
| 24 | 3802396 |
| 25 | 10360559 |
| 26 | 18819920 |
| 27 | 37639840 |
| 28 | 102558961 |
| 29 | 186298002 |
[0,0,0,1,2,4,11,20,40,109,198,396,1079,1960,3920, 10681,19402,38804,105731,192060,384120,1046629, 1901198,3802396,10360559,18819920,37639840, 102558961,186298002] |