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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 4 |
| 4 | 10 |
| 5 | 28 |
| 6 | 80 |
| 7 | 244 |
| 8 | 732 |
| 9 | 2320 |
| 10 | 7172 |
| 11 | 23212 |
| 12 | 73228 |
| 13 | 240184 |
| 14 | 768932 |
| 15 | 2545568 |
| 16 | 8240604 |
| 17 | 27468352 |
| 18 | 89699652 |
| 19 | 300579836 |
| 20 | 988463844 |
[1,2,4,10,28,80,244,732,2320,7172,23212,73228, 240184,768932,2545568,8240604,27468352,89699652, 300579836,988463844] |