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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 15 |
| 3 | 87 |
| 4 | 513 |
| 5 | 3387 |
| 6 | 21933 |
| 7 | 141411 |
| 8 | 913245 |
| 9 | 5898099 |
| 10 | 38088477 |
| 11 | 245968275 |
| 12 | 1588424445 |
| 13 | 10257784563 |
| 14 | 66243081501 |
| 15 | 427786930899 |
| 16 | 2762577674301 |
| 17 | 17840272397235 |
| 18 | 115209545904477 |
| 19 | 744004305214611 |
| 20 | 4804657476983421 |
[0,15,87,513,3387,21933,141411,913245,5898099, 38088477,245968275,1588424445,10257784563, 66243081501,427786930899,2762577674301, 17840272397235,115209545904477,744004305214611, 4804657476983421] |