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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 7 |
| 5 | 18 |
| 6 | 68 |
| 7 | 251 |
| 8 | 1020 |
| 9 | 4258 |
| 10 | 18580 |
| 11 | 82716 |
| 12 | 377207 |
| 13 | 1748250 |
| 14 | 8227066 |
| 15 | 39197164 |
| 16 | 188824506 |
| 17 | 918333933 |
| 18 | 4504366940 |
| 19 | 22260929867 |
| 20 | 110763984273 |
| 21 | 554510459987 |
| 22 | 2791460440109 |
| 23 | 14123739733754 |
| 24 | 71792405634223 |
| 25 | 366483503897357 |
| 26 | 1878163540497162 |
| 27 | 9660232634407657 |
[1,1,1,2,7,18,68,251,1020,4258,18580,82716,377207, 1748250,8227066,39197164,188824506,918333933, 4504366940,22260929867,110763984273,554510459987, 2791460440109,14123739733754,71792405634223, 366483503897357,1878163540497162,9660232634407657] |