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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 13 |
| 3 | 80 |
| 4 | 481 |
| 5 | 2888 |
| 6 | 17329 |
| 7 | 103976 |
| 8 | 623857 |
| 9 | 3743144 |
| 10 | 22458865 |
| 11 | 134753192 |
| 12 | 808519153 |
| 13 | 4851114920 |
| 14 | 29106689521 |
| 15 | 174640137128 |
| 16 | 1047840822769 |
| 17 | 6287044936616 |
| 18 | 37722269619697 |
| 19 | 226333617718184 |
| 20 | 1358001706309105 |
[2,13,80,481,2888,17329,103976,623857,3743144, 22458865,134753192,808519153,4851114920, 29106689521,174640137128,1047840822769, 6287044936616,37722269619697,226333617718184, 1358001706309105] |