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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 7 |
| 2 | 28 |
| 3 | 119 |
| 4 | 616 |
| 5 | 3367 |
| 6 | 19684 |
| 7 | 117655 |
| 8 | 720916 |
| 9 | 4483815 |
| 10 | 28249228 |
| 11 | 179756983 |
| 12 | 1153450872 |
| 13 | 7453000807 |
| 14 | 48444564052 |
| 15 | 316504102999 |
| 16 | 2077058521216 |
| 17 | 13684147881607 |
| 18 | 90467424361132 |
| 19 | 599941851861751 |
| 20 | 3989613329006536 |
| 21 | 26597422099282535 |
[1,7,28,119,616,3367,19684,117655,720916,4483815, 28249228,179756983,1153450872,7453000807, 48444564052,316504102999,2077058521216, 13684147881607,90467424361132,599941851861751, 3989613329006536,26597422099282535] |