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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 4 |
| 3 | 15 |
| 4 | 52 |
| 5 | 170 |
| 6 | 603 |
| 7 | 2157 |
| 8 | 7777 |
| 9 | 28195 |
| 10 | 102429 |
| 11 | 372430 |
| 12 | 1355019 |
| 13 | 4930977 |
| 14 | 17946466 |
| 15 | 65320396 |
| 16 | 237756751 |
| 17 | 865411414 |
| 18 | 3150039989 |
| 19 | 11465974491 |
| 20 | 41735611962 |
| 21 | 151915810407 |
| 22 | 552967220870 |
| 23 | 2012778077066 |
| 24 | 7326430841669 |
[2,4,15,52,170,603,2157,7777,28195,102429,372430, 1355019,4930977,17946466,65320396,237756751, 865411414,3150039989,11465974491,41735611962, 151915810407,552967220870,2012778077066, 7326430841669] |