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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 4 |
| 3 | 14 |
| 4 | 47 |
| 5 | 151 |
| 6 | 474 |
| 7 | 1457 |
| 8 | 4414 |
| 9 | 13210 |
| 10 | 39155 |
| 11 | 115120 |
| 12 | 336183 |
| 13 | 976070 |
| 14 | 2819785 |
| 15 | 8110657 |
| 16 | 23239662 |
| 17 | 66362960 |
| 18 | 188930728 |
| 19 | 536407146 |
| 20 | 1519205230 |
| 21 | 4293061640 |
| 22 | 12106883585 |
| 23 | 34079016842 |
| 24 | 95762829405 |
| 25 | 268670620736 |
| 26 | 752676269695 |
| 27 | 2105751165046 |
| 28 | 5883798478398 |
[0,1,4,14,47,151,474,1457,4414,13210,39155,115120, 336183,976070,2819785,8110657,23239662,66362960, 188930728,536407146,1519205230,4293061640, 12106883585,34079016842,95762829405,268670620736, 752676269695,2105751165046,5883798478398] |