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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 20 |
| 5 | 73 |
| 6 | 272 |
| 7 | 1040 |
| 8 | 4177 |
| 9 | 17264 |
| 10 | 72861 |
| 11 | 311631 |
| 12 | 1349356 |
| 13 | 5922851 |
| 14 | 26295985 |
| 15 | 117817978 |
| 16 | 531665582 |
| 17 | 2415053676 |
| 18 | 11040435677 |
| 19 | 50762362640 |
| 20 | 234552661491 |
| 21 | 1088404398909 |
| 22 | 5070457777960 |
| 23 | 23708810322816 |
| 24 | 111236246629822 |
| 25 | 523484373005358 |
| 26 | 2470328346542832 |
| 27 | 11687294570928665 |
| 28 | 55425802377348044 |
[1,1,2,6,20,73,272,1040,4177,17264,72861,311631, 1349356,5922851,26295985,117817978,531665582, 2415053676,11040435677,50762362640,234552661491, 1088404398909,5070457777960,23708810322816, 111236246629822,523484373005358,2470328346542832, 11687294570928665,55425802377348044] |