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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 2 |
| 4 | 48 |
| 5 | 526 |
| 6 | 3450 |
| 7 | 16536 |
| 8 | 63104 |
| 9 | 204202 |
| 10 | 580669 |
| 11 | 1491096 |
| 12 | 3520768 |
| 13 | 7754502 |
| 14 | 16098425 |
| 15 | 31770760 |
| 16 | 59998736 |
| 17 | 109022244 |
| 18 | 191454654 |
| 19 | 326158974 |
| 20 | 540703008 |
| 21 | 874630262 |
| 22 | 1383621756 |
| 23 | 2144889472 |
| 24 | 3263884272 |
| 25 | 4882793214 |
| 26 | 7190910467 |
| 27 | 10437526372 |
| 28 | 14947411024 |
[0,0,2,48,526,3450,16536,63104,204202,580669, 1491096,3520768,7754502,16098425,31770760, 59998736,109022244,191454654,326158974,540703008, 874630262,1383621756,2144889472,3263884272, 4882793214,7190910467,10437526372,14947411024] |