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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 4 |
| 4 | 7 |
| 5 | 26 |
| 6 | 87 |
| 7 | 226 |
| 8 | 800 |
| 9 | 2424 |
| 10 | 9975 |
| 11 | 40045 |
| 12 | 152852 |
| 13 | 626232 |
| 14 | 2317403 |
| 15 | 9962949 |
| 16 | 43599477 |
| 17 | 179247754 |
| 18 | 777881238 |
[1,2,4,7,26,87,226,800,2424,9975,40045,152852, 626232,2317403,9962949,43599477,179247754, 777881238] |