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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 2 |
| 2 | 4 |
| 3 | 12 |
| 4 | 42 |
| 5 | 130 |
| 6 | 404 |
| 7 | 1282 |
| 8 | 4044 |
| 9 | 12726 |
| 10 | 40114 |
| 11 | 126450 |
| 12 | 398478 |
| 13 | 1255796 |
| 14 | 3957784 |
| 15 | 12473128 |
| 16 | 39309510 |
| 17 | 123885908 |
| 18 | 390432440 |
| 19 | 1230465890 |
| 20 | 3877871274 |
| 21 | 12221294900 |
| 22 | 38515986858 |
| 23 | 121384948432 |
| 24 | 382550391954 |
| 25 | 1205625604758 |
| 26 | 3799585957042 |
| 27 | 11974574363290 |
[0,2,4,12,42,130,404,1282,4044,12726,40114,126450, 398478,1255796,3957784,12473128,39309510, 123885908,390432440,1230465890,3877871274, 12221294900,38515986858,121384948432,382550391954, 1205625604758,3799585957042,11974574363290] |