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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 7 |
| 3 | 20 |
| 4 | 53 |
| 5 | 143 |
| 6 | 385 |
| 7 | 1036 |
| 8 | 2789 |
| 9 | 7507 |
| 10 | 20207 |
| 11 | 54392 |
| 12 | 146409 |
| 13 | 394095 |
| 14 | 1060801 |
| 15 | 2855400 |
| 16 | 7685993 |
| 17 | 20688691 |
| 18 | 55688567 |
| 19 | 149899116 |
| 20 | 403489373 |
| 21 | 1086088287 |
| 22 | 2923466753 |
| 23 | 7869210964 |
| 24 | 21181866061 |
| 25 | 57016065763 |
| 26 | 153472396895 |
[1,3,7,20,53,143,385,1036,2789,7507,20207,54392, 146409,394095,1060801,2855400,7685993,20688691, 55688567,149899116,403489373,1086088287, 2923466753,7869210964,21181866061,57016065763, 153472396895] |