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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 3 |
| 5 | 6 |
| 6 | 13 |
| 7 | 36 |
| 8 | 93 |
| 9 | 243 |
| 10 | 645 |
| 11 | 1782 |
| 12 | 4914 |
| 13 | 13608 |
| 14 | 37890 |
| 15 | 106288 |
| 16 | 299025 |
| 17 | 844182 |
| 18 | 2391363 |
| 19 | 6797196 |
| 20 | 19371684 |
| 21 | 55345784 |
| 22 | 158486625 |
| 23 | 454795398 |
| 24 | 1307541690 |
| 25 | 3765720066 |
| 26 | 10862647236 |
| 27 | 31381059609 |
| 28 | 90780960426 |
| 29 | 262951692390 |
[0,0,1,3,6,13,36,93,243,645,1782,4914,13608,37890, 106288,299025,844182,2391363,6797196,19371684, 55345784,158486625,454795398,1307541690, 3765720066,10862647236,31381059609,90780960426, 262951692390] |