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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 20 |
| 3 | 143 |
| 4 | 986 |
| 5 | 6764 |
| 6 | 46367 |
| 7 | 317810 |
| 8 | 2178308 |
| 9 | 14930351 |
| 10 | 102334154 |
| 11 | 701408732 |
| 12 | 4807526975 |
| 13 | 32951280098 |
| 14 | 225851433716 |
| 15 | 1548008755919 |
| 16 | 10610209857722 |
| 17 | 72723460248140 |
| 18 | 498454011879263 |
| 19 | 3416454622906706 |
| 20 | 23416728348467684 |
| 21 | 160500643816367087 |
[2,20,143,986,6764,46367,317810,2178308,14930351, 102334154,701408732,4807526975,32951280098, 225851433716,1548008755919,10610209857722, 72723460248140,498454011879263,3416454622906706, 23416728348467684,160500643816367087] |