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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 3 |
| 3 | 0 |
| 4 | 8 |
| 5 | 20 |
| 6 | 66 |
| 7 | 207 |
| 8 | 726 |
| 9 | 2461 |
| 10 | 8538 |
| 11 | 29072 |
| 12 | 100909 |
| 13 | 345464 |
| 14 | 1192462 |
| 15 | 4104543 |
| 16 | 14145598 |
| 17 | 48741105 |
| 18 | 167919091 |
| 19 | 578641035 |
| 20 | 1993746222 |
| 21 | 6869984946 |
| 22 | 23672540436 |
| 23 | 81569450595 |
| 24 | 281073069448 |
| 25 | 968513250894 |
| 26 | 3337304064491 |
| 27 | 11499656306463 |
[0,3,0,8,20,66,207,726,2461,8538,29072,100909, 345464,1192462,4104543,14145598,48741105, 167919091,578641035,1993746222,6869984946, 23672540436,81569450595,281073069448,968513250894, 3337304064491,11499656306463] |