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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 6 |
| 5 | 27 |
| 6 | 106 |
| 7 | 387 |
| 8 | 1350 |
| 9 | 4566 |
| 10 | 15102 |
| 11 | 49113 |
| 12 | 157622 |
| 13 | 500520 |
| 14 | 1575558 |
| 15 | 4923536 |
| 16 | 15290784 |
| 17 | 47235771 |
| 18 | 145246224 |
| 19 | 444814533 |
| 20 | 1357368786 |
| 21 | 4128880561 |
| 22 | 12523521786 |
| 23 | 37888119522 |
| 24 | 114358226428 |
| 25 | 344437708131 |
| 26 | 1035409733820 |
[0,0,0,1,6,27,106,387,1350,4566,15102,49113, 157622,500520,1575558,4923536,15290784,47235771, 145246224,444814533,1357368786,4128880561, 12523521786,37888119522,114358226428,344437708131, 1035409733820] |