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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 12 |
| 4 | 34 |
| 5 | 100 |
| 6 | 292 |
| 7 | 852 |
| 8 | 2488 |
| 9 | 7264 |
| 10 | 21208 |
| 11 | 61920 |
| 12 | 180784 |
| 13 | 527824 |
| 14 | 1541056 |
| 15 | 4499328 |
| 16 | 13136416 |
| 17 | 38353600 |
| 18 | 111978688 |
| 19 | 326937408 |
| 20 | 954539392 |
| 21 | 2786910976 |
| 22 | 8136775552 |
| 23 | 23756451840 |
| 24 | 69360276736 |
| 25 | 202507008256 |
| 26 | 591247473664 |
| 27 | 1726229517312 |
| 28 | 5039967998464 |
[1,1,4,12,34,100,292,852,2488,7264,21208,61920, 180784,527824,1541056,4499328,13136416,38353600, 111978688,326937408,954539392,2786910976, 8136775552,23756451840,69360276736,202507008256, 591247473664,1726229517312,5039967998464] |