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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 15 |
| 5 | 44 |
| 6 | 138 |
| 7 | 444 |
| 8 | 1474 |
| 9 | 5000 |
| 10 | 17240 |
| 11 | 60260 |
| 12 | 213012 |
| 13 | 760140 |
| 14 | 2734700 |
| 15 | 9907857 |
| 16 | 36117810 |
| 17 | 132379490 |
| 18 | 487546557 |
| 19 | 1803381000 |
| 20 | 6696499910 |
| 21 | 24953813577 |
| 22 | 93285944640 |
| 23 | 349756113560 |
| 24 | 1314857960901 |
| 25 | 4955232346092 |
| 26 | 18717109185712 |
| 27 | 70848408876905 |
[1,1,2,6,15,44,138,444,1474,5000,17240,60260, 213012,760140,2734700,9907857,36117810,132379490, 487546557,1803381000,6696499910,24953813577, 93285944640,349756113560,1314857960901, 4955232346092,18717109185712,70848408876905] |