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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 74 |
| 5 | 274 |
| 6 | 1103 |
| 7 | 4366 |
| 8 | 18185 |
| 9 | 75130 |
| 10 | 320070 |
| 11 | 1357859 |
| 12 | 5878960 |
| 13 | 25424127 |
| 14 | 111353321 |
| 15 | 488593653 |
| 16 | 2159883504 |
| 17 | 9580510260 |
| 18 | 42685811494 |
| 19 | 190927066056 |
| 20 | 856389848702 |
| 21 | 3855864378779 |
| 22 | 17395678174933 |
| 23 | 78741818484017 |
| 24 | 357039584129968 |
| 25 | 1623322577244383 |
| 26 | 7392971454270849 |
| 27 | 33740927962862991 |
[1,2,6,20,74,274,1103,4366,18185,75130,320070, 1357859,5878960,25424127,111353321,488593653, 2159883504,9580510260,42685811494,190927066056, 856389848702,3855864378779,17395678174933, 78741818484017,357039584129968,1623322577244383, 7392971454270849,33740927962862991] |