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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 2 |
| 4 | 6 |
| 5 | 18 |
| 6 | 54 |
| 7 | 152 |
| 8 | 422 |
| 9 | 1160 |
| 10 | 3156 |
| 11 | 8534 |
| 12 | 22968 |
| 13 | 61578 |
| 14 | 164602 |
| 15 | 438930 |
| 16 | 1168120 |
| 17 | 3103540 |
| 18 | 8234122 |
| 19 | 21820098 |
| 20 | 57762774 |
| 21 | 152774358 |
| 22 | 403750258 |
| 23 | 1066291206 |
| 24 | 2814322014 |
| 25 | 7423962336 |
| 26 | 19574314938 |
| 27 | 51587866820 |
| 28 | 135905559330 |
| 29 | 357908155044 |
[0,0,0,2,6,18,54,152,422,1160,3156,8534,22968, 61578,164602,438930,1168120,3103540,8234122, 21820098,57762774,152774358,403750258,1066291206, 2814322014,7423962336,19574314938,51587866820, 135905559330,357908155044] |