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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 21 |
| 3 | 145 |
| 4 | 1122 |
| 5 | 7886 |
| 6 | 58446 |
| 7 | 405196 |
| 8 | 2865756 |
| 9 | 19652430 |
| 10 | 135666717 |
| 11 | 917861737 |
| 12 | 6247996468 |
| 13 | 41874859669 |
| 14 | 281884085368 |
| 15 | 1877330322718 |
| 16 | 12537690094009 |
| 17 | 83063782595536 |
| 18 | 551574419251898 |
| 19 | 3639691674489757 |
| 20 | 24059481994135080 |
[1,21,145,1122,7886,58446,405196,2865756,19652430, 135666717,917861737,6247996468,41874859669, 281884085368,1877330322718,12537690094009, 83063782595536,551574419251898,3639691674489757, 24059481994135080] |