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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 6 |
| 5 | 27 |
| 6 | 122 |
| 7 | 516 |
| 8 | 2148 |
| 9 | 8792 |
| 10 | 35622 |
| 11 | 143079 |
| 12 | 570830 |
| 13 | 2264649 |
| 14 | 8942436 |
| 15 | 35169616 |
| 16 | 137839308 |
| 17 | 538594704 |
| 18 | 2098892928 |
| 19 | 8159937669 |
| 20 | 31656305550 |
| 21 | 122575164923 |
| 22 | 473797120338 |
| 23 | 1828512928200 |
| 24 | 7046581314292 |
| 25 | 27119735418924 |
| 26 | 104247226432566 |
| 27 | 400272672674603 |
[0,0,1,6,27,122,516,2148,8792,35622,143079,570830, 2264649,8942436,35169616,137839308,538594704, 2098892928,8159937669,31656305550,122575164923, 473797120338,1828512928200,7046581314292, 27119735418924,104247226432566,400272672674603] |