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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 72 |
| 5 | 270 |
| 6 | 1040 |
| 7 | 4036 |
| 8 | 15714 |
| 9 | 61226 |
| 10 | 238778 |
| 11 | 930716 |
| 12 | 3628520 |
| 13 | 14143922 |
| 14 | 55134174 |
| 15 | 214941488 |
| 16 | 838158510 |
| 17 | 3269630046 |
| 18 | 12761106790 |
| 19 | 49834920864 |
| 20 | 194743761948 |
| 21 | 761543265544 |
| 22 | 2980128724806 |
| 23 | 11670402459630 |
| 24 | 45734346816026 |
| 25 | 179348093549914 |
| 26 | 703781965002650 |
[1,2,6,20,72,270,1040,4036,15714,61226,238778, 930716,3628520,14143922,55134174,214941488, 838158510,3269630046,12761106790,49834920864, 194743761948,761543265544,2980128724806, 11670402459630,45734346816026,179348093549914, 703781965002650] |