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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 12 |
| 4 | 50 |
| 5 | 187 |
| 6 | 801 |
| 7 | 3367 |
| 8 | 14750 |
| 9 | 64496 |
| 10 | 288283 |
| 11 | 1298078 |
| 12 | 5916459 |
| 13 | 27107847 |
| 14 | 125107445 |
| 15 | 580279403 |
| 16 | 2704828242 |
| 17 | 12656086712 |
| 18 | 59445058605 |
| 19 | 280159509962 |
| 20 | 1324504668796 |
| 21 | 6278619362700 |
| 22 | 29835818846267 |
| 23 | 142094119428556 |
| 24 | 678102617877031 |
| 25 | 3242027299595844 |
| 26 | 15526944664613450 |
| 27 | 74482919169897600 |
[1,1,4,12,50,187,801,3367,14750,64496,288283, 1298078,5916459,27107847,125107445,580279403, 2704828242,12656086712,59445058605,280159509962, 1324504668796,6278619362700,29835818846267, 142094119428556,678102617877031,3242027299595844, 15526944664613450,74482919169897600] |