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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 4 |
| 3 | 6 |
| 4 | 20 |
| 5 | 49 |
| 6 | 132 |
| 7 | 344 |
| 8 | 908 |
| 9 | 2384 |
| 10 | 6273 |
| 11 | 16492 |
| 12 | 43372 |
| 13 | 114050 |
| 14 | 299916 |
| 15 | 788673 |
| 16 | 2073944 |
| 17 | 5453760 |
| 18 | 14341528 |
| 19 | 37713312 |
| 20 | 99173121 |
| 21 | 260791400 |
| 22 | 685792228 |
| 23 | 1803399102 |
| 24 | 4742323108 |
| 25 | 12470688497 |
| 26 | 32793647356 |
| 27 | 86236081272 |
| 28 | 226771411940 |
| 29 | 596331286320 |
[1,0,4,6,20,49,132,344,908,2384,6273,16492,43372, 114050,299916,788673,2073944,5453760,14341528, 37713312,99173121,260791400,685792228,1803399102, 4742323108,12470688497,32793647356,86236081272, 226771411940,596331286320] |