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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 4 |
| 3 | 13 |
| 4 | 38 |
| 5 | 113 |
| 6 | 336 |
| 7 | 1001 |
| 8 | 2994 |
| 9 | 8965 |
| 10 | 26868 |
| 11 | 80565 |
| 12 | 241630 |
| 13 | 724793 |
| 14 | 2174232 |
| 15 | 6522465 |
| 16 | 19567050 |
| 17 | 58700621 |
| 18 | 176101052 |
| 19 | 528301933 |
| 20 | 1584903926 |
| 21 | 4754708929 |
| 22 | 14264122464 |
| 23 | 42792360793 |
| 24 | 128377072354 |
| 25 | 385131201813 |
| 26 | 1155393582212 |
| 27 | 3466180711333 |
| 28 | 10398542080270 |
[0,1,4,13,38,113,336,1001,2994,8965,26868,80565, 241630,724793,2174232,6522465,19567050,58700621, 176101052,528301933,1584903926,4754708929, 14264122464,42792360793,128377072354,385131201813, 1155393582212,3466180711333,10398542080270] |