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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 4 |
| 3 | 23 |
| 4 | 122 |
| 5 | 199 |
| 6 | 408 |
| 7 | 4995 |
| 8 | 7320 |
| 9 | 44217 |
| 10 | 177682 |
| 11 | 394826 |
| 12 | 1706886 |
| 13 | 1738064 |
| 14 | 8403388 |
| 15 | 21194961 |
| 16 | 110525339 |
| 17 | 314033376 |
| 18 | 328840890 |
[2,4,23,122,199,408,4995,7320,44217,177682,394826, 1706886,1738064,8403388,21194961,110525339, 314033376,328840890] |