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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 4 |
| 4 | 10 |
| 5 | 23 |
| 6 | 63 |
| 7 | 155 |
| 8 | 448 |
| 9 | 1152 |
| 10 | 3452 |
| 11 | 9158 |
| 12 | 28178 |
| 13 | 76539 |
| 14 | 240370 |
| 15 | 665129 |
| 16 | 2123439 |
| 17 | 5964691 |
| 18 | 19302315 |
| 19 | 54898415 |
| 20 | 179696520 |
[1,1,2,4,10,23,63,155,448,1152,3452,9158,28178, 76539,240370,665129,2123439,5964691,19302315, 54898415,179696520] |