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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 70 |
| 5 | 251 |
| 6 | 911 |
| 7 | 3327 |
| 8 | 12190 |
| 9 | 44744 |
| 10 | 164407 |
| 11 | 604487 |
| 12 | 2223504 |
| 13 | 8181175 |
| 14 | 30108147 |
| 15 | 110820165 |
| 16 | 407946421 |
| 17 | 1501844193 |
| 18 | 5529362694 |
| 19 | 20358557249 |
| 20 | 74961030414 |
| 21 | 276017648570 |
| 22 | 1016360893036 |
| 23 | 3742540945813 |
| 24 | 13781324308298 |
| 25 | 50748099850042 |
[1,2,6,20,70,251,911,3327,12190,44744,164407, 604487,2223504,8181175,30108147,110820165, 407946421,1501844193,5529362694,20358557249, 74961030414,276017648570,1016360893036, 3742540945813,13781324308298,50748099850042] |