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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 4 |
| 4 | 12 |
| 5 | 36 |
| 6 | 100 |
| 7 | 288 |
| 8 | 805 |
| 9 | 2288 |
| 10 | 6471 |
| 11 | 18420 |
| 12 | 52426 |
| 13 | 149832 |
| 14 | 428649 |
| 15 | 1229354 |
| 16 | 3530715 |
| 17 | 10157552 |
| 18 | 29259703 |
| 19 | 84396168 |
| 20 | 243698332 |
| 21 | 704436640 |
| 22 | 2038158801 |
| 23 | 5902222810 |
| 24 | 17105674632 |
| 25 | 49612191480 |
| 26 | 143990912750 |
| 27 | 418177092554 |
[0,1,4,12,36,100,288,805,2288,6471,18420,52426, 149832,428649,1229354,3530715,10157552,29259703, 84396168,243698332,704436640,2038158801, 5902222810,17105674632,49612191480,143990912750, 418177092554] |