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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 12 |
| 4 | 38 |
| 5 | 90 |
| 6 | 220 |
| 7 | 460 |
| 8 | 1018 |
| 9 | 2022 |
| 10 | 4304 |
| 11 | 8376 |
| 12 | 17566 |
| 13 | 33922 |
| 14 | 70756 |
| 15 | 136260 |
| 16 | 283682 |
| 17 | 545790 |
| 18 | 1135576 |
| 19 | 2184112 |
| 20 | 4543366 |
| 21 | 8737626 |
| 22 | 18174764 |
| 23 | 34951932 |
| 24 | 72700618 |
| 25 | 139809430 |
| 26 | 290804320 |
| 27 | 559239720 |
| 28 | 1163219438 |
[1,1,4,12,38,90,220,460,1018,2022,4304,8376,17566, 33922,70756,136260,283682,545790,1135576,2184112, 4543366,8737626,18174764,34951932,72700618, 139809430,290804320,559239720,1163219438] |