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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 1 |
| 3 | 1 |
| 4 | 4 |
| 5 | 12 |
| 6 | 42 |
| 7 | 147 |
| 8 | 527 |
| 9 | 1914 |
| 10 | 7039 |
| 11 | 26159 |
| 12 | 98110 |
| 13 | 370919 |
| 14 | 1412211 |
| 15 | 5410273 |
| 16 | 20841886 |
| 17 | 80685792 |
| 18 | 313747624 |
| 19 | 1224895416 |
| 20 | 4799435482 |
| 21 | 18867423751 |
| 22 | 74394859297 |
| 23 | 294152650731 |
| 24 | 1166021396660 |
| 25 | 4632969618849 |
| 26 | 18448290723435 |
[1,0,1,1,4,12,42,147,527,1914,7039,26159,98110, 370919,1412211,5410273,20841886,80685792, 313747624,1224895416,4799435482,18867423751, 74394859297,294152650731,1166021396660, 4632969618849,18448290723435] |