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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 1 |
| 5 | 6 |
| 6 | 12 |
| 7 | 42 |
| 8 | 107 |
| 9 | 323 |
| 10 | 888 |
| 11 | 2568 |
| 12 | 7224 |
| 13 | 20629 |
| 14 | 58429 |
| 15 | 166230 |
| 16 | 471780 |
| 17 | 1340730 |
| 18 | 3807431 |
| 19 | 10816631 |
| 20 | 30722736 |
| 21 | 87272592 |
| 22 | 247895472 |
| 23 | 704164537 |
| 24 | 2000191753 |
| 25 | 5681637318 |
| 26 | 16138865148 |
| 27 | 45843078954 |
| 28 | 130218850259 |
[0,0,0,1,1,6,12,42,107,323,888,2568,7224,20629, 58429,166230,471780,1340730,3807431,10816631, 30722736,87272592,247895472,704164537,2000191753, 5681637318,16138865148,45843078954,130218850259] |