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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 20 |
| 3 | 100 |
| 4 | 590 |
| 5 | 2102 |
| 6 | 13190 |
| 7 | 40646 |
| 8 | 233696 |
| 9 | 865756 |
| 10 | 4191364 |
| 11 | 12656548 |
| 12 | 88372916 |
| 13 | 233981316 |
| 14 | 1196779716 |
| 15 | 4919600196 |
| 16 | 23553092286 |
| 17 | 65558004246 |
| 18 | 419488280946 |
| 19 | 1126393556946 |
| 20 | 6915947767386 |
| 21 | 24140199749466 |
| 22 | 99887762443386 |
| 23 | 297490099905786 |
| 24 | 2232346320891786 |
| 25 | 6151075120462098 |
[2,20,100,590,2102,13190,40646,233696,865756, 4191364,12656548,88372916,233981316,1196779716, 4919600196,23553092286,65558004246,419488280946, 1126393556946,6915947767386,24140199749466, 99887762443386,297490099905786,2232346320891786, 6151075120462098] |