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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 18 |
| 4 | 52 |
| 5 | 154 |
| 6 | 452 |
| 7 | 1330 |
| 8 | 3912 |
| 9 | 11506 |
| 10 | 33844 |
| 11 | 99546 |
| 12 | 292800 |
| 13 | 861226 |
| 14 | 2533164 |
| 15 | 7450914 |
| 16 | 21915720 |
| 17 | 64461730 |
| 18 | 189604292 |
| 19 | 557691946 |
| 20 | 1640365328 |
| 21 | 4824883034 |
| 22 | 14191653468 |
| 23 | 41742572146 |
| 24 | 122779374040 |
| 25 | 361136698450 |
| 26 | 1062228212084 |
[1,2,6,18,52,154,452,1330,3912,11506,33844,99546, 292800,861226,2533164,7450914,21915720,64461730, 189604292,557691946,1640365328,4824883034, 14191653468,41742572146,122779374040,361136698450, 1062228212084] |