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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 4 |
| 4 | 10 |
| 5 | 28 |
| 6 | 100 |
| 7 | 421 |
| 8 | 2101 |
| 9 | 11953 |
| 10 | 76121 |
| 11 | 533780 |
| 12 | 4077565 |
| 13 | 33655662 |
| 14 | 298278708 |
| 15 | 2824175781 |
| 16 | 28446451346 |
| 17 | 303704165521 |
| 18 | 3425895062137 |
| 19 | 40716009508038 |
| 20 | 508528878864884 |
[1,2,4,10,28,100,421,2101,11953,76121,533780, 4077565,33655662,298278708,2824175781,28446451346, 303704165521,3425895062137,40716009508038, 508528878864884] |